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BASH(1)                                                                                              BASH(1)



NAME
       bash - GNU Bourne-Again SHell

SYNOPSIS
       bash [options] [file]

COPYRIGHT
       Bash is Copyright (C) 1989-2005 by the Free Software Foundation, Inc.

DESCRIPTION
       Bash  is  an sh-compatible command language interpreter that executes commands read from the standard
       input or from a file.  Bash also incorporates useful features from the Korn and  C  shells  (ksh  and
       csh).

       Bash  is  intended  to  be a conformant implementation of the Shell and Utilities portion of the IEEE
       POSIX specification (IEEE Standard 1003.1).   Bash  can  be  configured  to  be  POSIX-conformant  by
       default.

OPTIONS
       In  addition  to  the single-character shell options documented in the description of the set builtin
       command, bash interprets the following options when it is invoked:

       -c string If the -c option is present, then commands are read from string.  If  there  are  arguments
                 after the string, they are assigned to the positional parameters, starting with $0.
       -i        If the -i option is present, the shell is interactive.
       -l        Make bash act as if it had been invoked as a login shell (see INVOCATION below).
       -r        If the -r option is present, the shell becomes restricted (see RESTRICTED SHELL below).
       -s        If  the  -s option is present, or if no arguments remain after option processing, then com-mands commands
                 mands are read from the standard input.  This option allows the positional parameters to be
                 set when invoking an interactive shell.
       -D        A list of all double-quoted strings preceded by $ is printed on the standard output.  These
                 are the strings that are subject to language translation when the current locale is  not  C
                 or POSIX.  This implies the -n option; no commands will be executed.
       [-+]O [shopt_option]
                 shopt_option  is  one of the shell options accepted by the shopt builtin (see SHELL BUILTIN
                 COMMANDS below).  If shopt_option is present, -O sets the value of that option;  +O  unsets
                 it.  If shopt_option is not supplied, the names and values of the shell options accepted by
                 shopt are printed on the standard output.  If the invocation option is +O,  the  output  is
                 displayed in a format that may be reused as input.
       --        A  --  signals  the  end  of options and disables further option processing.  Any arguments
                 after the -- are treated as filenames and arguments.  An argument of - is equivalent to --.

       Bash  also  interprets a number of multi-character options.  These options must appear on the command
       line before the single-character options to be recognized.

       --debugger
              Arrange for the debugger profile to be executed before the shell starts.   Turns  on  extended
              debugging  mode  (see  the  description of the extdebug option to the shopt builtin below) and
              shell function tracing (see the description of the -o functrace  option  to  the  set  builtin
              below).
       --dump-po-strings
              Equivalent to -D, but the output is in the GNU gettext po (portable object) file format.
       --dump-strings
              Equivalent to -D.
       --help Display a usage message on standard output and exit successfully.
       --init-file file
       --rcfile file
              Execute  commands  from file instead of the standard personal initialization file ~/.bashrc if
              the shell is interactive (see INVOCATION below).

       --login
              Equivalent to -l.

       --noediting
              Do not use the GNU readline library to read command lines when the shell is interactive.

       --noprofile
              Do not read either the system-wide startup file /etc/profile or any of the  personal  initial-ization initialization
              ization  files  ~/.bash_profile,  ~/.bash_login,  or ~/.profile.  By default, bash reads these
              files when it is invoked as a login shell (see INVOCATION below).

       --norc Do not read and execute the personal initialization file ~/.bashrc if the  shell  is  interac-tive. interactive.
              tive.  This option is on by default if the shell is invoked as sh.

       --posix
              Change  the  behavior  of  bash where the default operation differs from the POSIX standard to
              match the standard (posix mode).

       --restricted
              The shell becomes restricted (see RESTRICTED SHELL below).

       --verbose
              Equivalent to  -v.

       --version
              Show version information for this instance of bash on the standard output  and  exit  success-fully. successfully.
              fully.

ARGUMENTS
       If  arguments remain after option processing, and neither the -c nor the -s option has been supplied,
       the first argument is assumed to be the name of a file containing shell commands.  If bash is invoked
       in  this  fashion,  $0  is  set to the name of the file, and the positional parameters are set to the
       remaining arguments.  Bash reads and executes commands from this file, then exits.  Bash's exit  sta-tus status
       tus  is the exit status of the last command executed in the script.  If no commands are executed, the
       exit status is 0.  An attempt is first made to open the file in the current  directory,  and,  if  no
       file is found, then the shell searches the directories in PATH for the script.

INVOCATION
       A  login  shell is one whose first character of argument zero is a -, or one started with the --login
       option.

       An interactive shell is one started without non-option arguments and  without  the  -c  option  whose
       standard input and error are both connected to terminals (as determined by isatty(3)), or one started
       with the -i option.  PS1 is set and $- includes i if bash is interactive, allowing a shell script  or
       a startup file to test this state.

       The following paragraphs describe how bash executes its startup files.  If any of the files exist but
       cannot be read, bash reports an error.  Tildes are expanded in file names as  described  below  under
       Tilde Expansion in the EXPANSION section.

       When  bash  is  invoked as an interactive login shell, or as a non-interactive shell with the --login
       option, it first reads and executes commands from the file /etc/profile, if that file exists.   After
       reading  that  file,  it looks for ~/.bash_profile, ~/.bash_login, and ~/.profile, in that order, and
       reads and executes commands from the first one that exists and is readable.  The  --noprofile  option
       may be used when the shell is started to inhibit this behavior.

       When  a  login  shell  exits,  bash  reads  and executes commands from the file ~/.bash_logout, if it
       exists.

       When an interactive shell that is not a login shell is started, bash reads and executes commands from
       ~/.bashrc, if that file exists.  This may be inhibited by using the --norc option.  The --rcfile file
       option will force bash to read and execute commands from file instead of ~/.bashrc.

       When bash is started non-interactively, to run a shell script, for example, it looks for the variable
       BASH_ENV  in  the  environment, expands its value if it appears there, and uses the expanded value as
       the name of a file to read and execute.  Bash behaves as if the following command were executed:
              if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi
       but the value of the PATH variable is not used to search for the file name.

       If bash is invoked with the name sh, it tries to mimic the startup behavior of historical versions of
       sh as closely as possible, while conforming to the POSIX standard as well.  When invoked as an inter-active interactive
       active login shell, or a non-interactive shell with the --login option, it first attempts to read and
       execute commands from /etc/profile and ~/.profile, in that order.  The --noprofile option may be used
       to inhibit this behavior.  When invoked as an interactive shell with the name sh, bash looks for  the
       variable  ENV,  expands its value if it is defined, and uses the expanded value as the name of a file
       to read and execute.  Since a shell invoked as sh does not attempt to read and execute commands  from
       any other startup files, the --rcfile option has no effect.  A non-interactive shell invoked with the
       name sh does not attempt to read any other startup files.  When invoked as sh, bash enters posix mode
       after the startup files are read.

       When  bash  is  started  in posix mode, as with the --posix command line option, it follows the POSIX
       standard for startup files.  In this mode, interactive shells expand the ENV  variable  and  commands
       are  read  and  executed  from the file whose name is the expanded value.  No other startup files are
       read.

       Bash attempts to determine when it is being run by the remote shell daemon, usually  rshd.   If  bash
       determines  it  is  being  run  by  rshd, it reads and executes commands from ~/.bashrc, if that file
       exists and is readable.  It will not do this if invoked as sh.  The --norc  option  may  be  used  to
       inhibit this behavior, and the --rcfile option may be used to force another file to be read, but rshd
       does not generally invoke the shell with those options or allow them to be specified.

       If the shell is started with the effective user (group) id not equal to the real user (group) id, and
       the  -p option is not supplied, no startup files are read, shell functions are not inherited from the
       environment, the SHELLOPTS variable, if it appears in the environment, is ignored, and the  effective
       user id is set to the real user id.  If the -p option is supplied at invocation, the startup behavior
       is the same, but the effective user id is not reset.

DEFINITIONS
       The following definitions are used throughout the rest of this document.
       blank  A space or tab.
       word   A sequence of characters considered as a single unit by the shell.  Also known as a token.
       name   A word consisting only of alphanumeric characters  and  underscores,  and  beginning  with  an
              alphabetic character or an underscore.  Also referred to as an identifier.
       metacharacter
              A character that, when unquoted, separates words.  One of the following:
              |  & ; ( ) < > space tab
       control operator
              A token that performs a control function.  It is one of the following symbols:
              || & && ; ;; ( ) | <newline>

RESERVED WORDS
       Reserved  words  are  words that have a special meaning to the shell.  The following words are recog-nized recognized
       nized as reserved when unquoted and either the first word of a  simple  command  (see  SHELL  GRAMMAR
       below) or the third word of a case or for command:

       ! case  do done elif else esac fi for function if in select then until while { } time [[ ]]

SHELL GRAMMAR
   Simple Commands
       A simple command is a sequence of optional variable assignments followed by blank-separated words and
       redirections, and terminated by a control operator.  The first word specifies the command to be  exe-cuted, executed,
       cuted,  and  is  passed as argument zero.  The remaining words are passed as arguments to the invoked
       command.

       The return value of a simple command is its exit status, or 128+n if the  command  is  terminated  by
       signal n.

   Pipelines
       A  pipeline  is  a  sequence  of one or more commands separated by the character |.  The format for a
       pipeline is:

              [time [-p]] [ ! ] command [ | command2 ... ]

       The standard output of command is connected via a pipe to the standard input of command2.  This  con-nection connection
       nection is performed before any redirections specified by the command (see REDIRECTION below).

       The return status of a pipeline is the exit status of the last command, unless the pipefail option is
       enabled.  If pipefail is enabled, the pipeline's return status is the value of the  last  (rightmost)
       command  to  exit with a non-zero status, or zero if all commands exit successfully.  If the reserved
       word !  precedes a pipeline, the exit status of that pipeline is the logical  negation  of  the  exit
       status  as  described  above.   The  shell waits for all commands in the pipeline to terminate before
       returning a value.

       If the time reserved word precedes a pipeline, the elapsed as well as user and system  time  consumed
       by  its execution are reported when the pipeline terminates.  The -p option changes the output format
       to that specified by POSIX.  The TIMEFORMAT variable may be set to a format string that specifies how
       the  timing  information should be displayed; see the description of TIMEFORMAT under Shell Variables
       below.

       Each command in a pipeline is executed as a separate process (i.e., in a subshell).

   Lists
       A list is a sequence of one or more pipelines separated by one of the operators ;, &, &&, or ||,  and
       optionally terminated by one of ;, &, or <newline>.

       Of  these  list  operators,  &&  and  || have equal precedence, followed by ; and &, which have equal
       precedence.

       A sequence of one or more newlines may appear in a list instead of a semicolon to delimit commands.

       If a command is terminated by the control operator &, the shell executes the  command  in  the  back-ground background
       ground in a subshell.  The shell does not wait for the command to finish, and the return status is 0.
       Commands separated by a ; are executed sequentially; the shell waits for each command to terminate in
       turn.  The return status is the exit status of the last command executed.

       The  control  operators  &&  and || denote AND lists and OR lists, respectively.  An AND list has the
       form

              command1 && command2

       command2 is executed if, and only if, command1 returns an exit status of zero.

       An OR list has the form

              command1 || command2


       command2 is executed if and only if command1 returns a non-zero exit status.  The  return  status  of
       AND and OR lists is the exit status of the last command executed in the list.

   Compound Commands
       A compound command is one of the following:

       (list) list  is  executed in a subshell environment (see COMMAND EXECUTION ENVIRONMENT below).  Vari-able Variable
              able assignments and builtin commands that affect the shell's environment  do  not  remain  in
              effect after the command completes.  The return status is the exit status of list.

       { list; }
              list is simply executed in the current shell environment.  list must be terminated with a new-line newline
              line or semicolon.  This is known as a group command.  The return status is the exit status of
              list.   Note that unlike the metacharacters ( and ), { and } are reserved words and must occur
              where a reserved word is permitted to be recognized.  Since they do not cause  a  word  break,
              they must be separated from list by whitespace.

       ((expression))
              The  expression  is  evaluated according to the rules described below under ARITHMETIC EVALUA-TION. EVALUATION.
              TION.  If the value of the expression is non-zero, the  return  status  is  0;  otherwise  the
              return status is 1.  This is exactly equivalent to let "expression".

       [[ expression ]]
              Return  a  status  of 0 or 1 depending on the evaluation of the conditional expression expres-sion. expression.
              sion.  Expressions are composed of the primaries described  below  under  CONDITIONAL  EXPRES-SIONS. EXPRESSIONS.
              SIONS.   Word  splitting  and pathname expansion are not performed on the words between the [[
              and ]]; tilde expansion, parameter and variable expansion, arithmetic expansion, command  sub-stitution, substitution,
              stitution,  process substitution, and quote removal are performed.  Conditional operators such
              as -f must be unquoted to be recognized as primaries.

              When the == and != operators are used, the string to the right of the operator is considered a
              pattern  and  matched  according  to the rules described below under Pattern Matching.  If the
              shell option nocasematch is enabled, the match is performed without  regard  to  the  case  of
              alphabetic  characters.   The  return  value is 0 if the string matches (==) or does not match
              (!=) the pattern, and 1 otherwise.  Any part of the pattern may be quoted to force  it  to  be
              matched as a string.

              An  additional binary operator, =~, is available, with the same precedence as == and !=.  When
              it is used, the string to the right of the operator is considered an extended regular  expres-sion expression
              sion  and  matched  accordingly (as in regex(3)).  The return value is 0 if the string matches
              the pattern, and 1 otherwise.  If the regular expression is syntactically incorrect, the  con-ditional conditional
              ditional  expression's  return  value  is  2.  If the shell option nocasematch is enabled, the
              match is performed without regard to the case of alphabetic characters.  Substrings matched by
              parenthesized  subexpressions  within  the  regular expression are saved in the array variable
              BASH_REMATCH.  The element of BASH_REMATCH with index 0 is the portion of the string  matching
              the entire regular expression.  The element of BASH_REMATCH with index n is the portion of the
              string matching the nth parenthesized subexpression.

              Expressions may be combined using the following  operators,  listed  in  decreasing  order  of
              precedence:

              ( expression )
                     Returns the value of expression.  This may be used to override the normal precedence of
                     operators.
              ! expression
                     True if expression is false.
              expression1 && expression2
                     True if both expression1 and expression2 are true.
              expression1 || expression2
                     True if either expression1 or expression2 is true.

              The && and || operators do not evaluate expression2 if the value of expression1 is  sufficient
              to determine the return value of the entire conditional expression.

       for name [ in word ] ; do list ; done
              The  list of words following in is expanded, generating a list of items.  The variable name is
              set to each element of this list in turn, and list is executed each time.  If the in  word  is
              omitted,  the  for  command  executes list once for each positional parameter that is set (see
              PARAMETERS below).  The return status is the exit status of the last  command  that  executes.
              If the expansion of the items following in results in an empty list, no commands are executed,
              and the return status is 0.

       for (( expr1 ; expr2 ; expr3 )) ; do list ; done
              First, the arithmetic expression expr1 is evaluated according to  the  rules  described  below
              under  ARITHMETIC  EVALUATION.   The  arithmetic expression expr2 is then evaluated repeatedly
              until it evaluates to zero.  Each time expr2 evaluates to a non-zero value, list  is  executed
              and the arithmetic expression expr3 is evaluated.  If any expression is omitted, it behaves as
              if it evaluates to 1.  The return value is the exit status of the last command in list that is
              executed, or false if any of the expressions is invalid.

       select name [ in word ] ; do list ; done
              The  list  of words following in is expanded, generating a list of items.  The set of expanded
              words is printed on the standard error, each preceded by a number.  If the in word is omitted,
              the  positional  parameters  are  printed (see PARAMETERS below).  The PS3 prompt is then dis-played displayed
              played and a line read from the standard input.  If the line consists of a number  correspond-ing corresponding
              ing to one of the displayed words, then the value of name is set to that word.  If the line is
              empty, the words and prompt are displayed again.  If EOF is read, the command completes.   Any
              other value read causes name to be set to null.  The line read is saved in the variable REPLY.
              The list is executed after each selection until a break command is executed.  The exit  status
              of select is the exit status of the last command executed in list, or zero if no commands were
              executed.

       case word in [ [(] pattern [ | pattern ] ... ) list ;; ] ... esac
              A case command first expands word, and tries to match it against each pattern in  turn,  using
              the same matching rules as for pathname expansion (see Pathname Expansion below).  The word is
              expanded using tilde expansion, parameter and  variable  expansion,  arithmetic  substitution,
              command  substitution,  process  substitution  and  quote  removal.   Each pattern examined is
              expanded using tilde expansion, parameter and  variable  expansion,  arithmetic  substitution,
              command  substitution,  and process substitution.  If the shell option nocasematch is enabled,
              the match is performed without regard to the case of alphabetic characters.  When a  match  is
              found,  the  corresponding list is executed.  After the first match, no subsequent matches are
              attempted.  The exit status is zero if no pattern matches.  Otherwise, it is the  exit  status
              of the last command executed in list.

       if list; then list; [ elif list; then list; ] ... [ else list; ] fi
              The  if  list is executed.  If its exit status is zero, the then list is executed.  Otherwise,
              each elif list is executed in turn, and if its exit status is  zero,  the  corresponding  then
              list is executed and the command completes.  Otherwise, the else list is executed, if present.
              The exit status is the exit status of the last command  executed,  or  zero  if  no  condition
              tested true.

       while list; do list; done
       until list; do list; done
              The  while  command  continuously  executes  the  do  list as long as the last command in list
              returns an exit status of zero.  The until command is identical to the while  command,  except
              that  the test is negated; the do list is executed as long as the last command in list returns
              a non-zero exit status.  The exit status of the while and until commands is the exit status of
              the last do list command executed, or zero if none was executed.

   Shell Function Definitions
       A  shell  function  is an object that is called like a simple command and executes a compound command
       with a new set of positional parameters.  Shell functions are declared as follows:

       [ function ] name () compound-command [redirection]
              This defines a function named name.  The reserved word function is optional.  If the  function
              reserved word is supplied, the parentheses are optional.  The body of the function is the com-pound compound
              pound command compound-command (see Compound Commands above).  That command is usually a  list
              of  commands  between  {  and  }, but may be any command listed under Compound Commands above.
              compound-command is executed whenever name is specified as the name of a simple command.   Any
              redirections  (see  REDIRECTION below) specified when a function is defined are performed when
              the function is executed.  The exit status of a function definition is zero  unless  a  syntax
              error  occurs  or  a  readonly function with the same name already exists.  When executed, the
              exit status of a function is the exit status of the last command executed in the  body.   (See
              FUNCTIONS below.)

COMMENTS
       In  a  non-interactive shell, or an interactive shell in which the interactive_comments option to the
       shopt builtin is enabled (see SHELL BUILTIN COMMANDS below), a word beginning with # causes that word
       and  all  remaining characters on that line to be ignored.  An interactive shell without the interac-tive_comments interactive_comments
       tive_comments option enabled does not allow comments.   The  interactive_comments  option  is  on  by
       default in interactive shells.

QUOTING
       Quoting  is  used to remove the special meaning of certain characters or words to the shell.  Quoting
       can be used to disable special treatment for special characters, to prevent reserved words from being
       recognized as such, and to prevent parameter expansion.

       Each  of  the metacharacters listed above under DEFINITIONS has special meaning to the shell and must
       be quoted if it is to represent itself.

       When the command history expansion facilities are being used (see HISTORY EXPANSION below), the  his-tory history
       tory expansion character, usually !, must be quoted to prevent history expansion.

       There are three quoting mechanisms: the escape character, single quotes, and double quotes.

       A non-quoted backslash (\) is the escape character.  It preserves the literal value of the next char-acter character
       acter that follows, with the exception of <newline>.  If a \<newline> pair appears, and the backslash
       is  not  itself quoted, the \<newline> is treated as a line continuation (that is, it is removed from
       the input stream and effectively ignored).

       Enclosing characters in single quotes preserves the  literal  value  of  each  character  within  the
       quotes.  A single quote may not occur between single quotes, even when preceded by a backslash.

       Enclosing  characters  in  double  quotes  preserves  the  literal value of all characters within the
       quotes, with the exception of $, `, \, and, when history expansion is enabled, !.  The  characters  $
       and  `  retain their special meaning within double quotes.  The backslash retains its special meaning
       only when followed by one of the following characters: $, `, ", \, or <newline>.  A double quote  may
       be  quoted within double quotes by preceding it with a backslash.  If enabled, history expansion will
       be performed unless an !  appearing in double quotes is escaped using  a  backslash.   The  backslash
       preceding the !  is not removed.

       The special parameters * and @ have special meaning when in double quotes (see PARAMETERS below).

       Words  of  the  form  $'string'  are  treated specially.  The word expands to string, with backslash-escaped backslashescaped
       escaped characters replaced as specified by the ANSI C  standard.   Backslash  escape  sequences,  if
       present, are decoded as follows:
              \a     alert (bell)
              \b     backspace
              \e     an escape character
              \f     form feed
              \n     new line
              \r     carriage return
              \t     horizontal tab
              \v     vertical tab
              \\     backslash
              \'     single quote
              \nnn   the eight-bit character whose value is the octal value nnn (one to three digits)
              \xHH   the eight-bit character whose value is the hexadecimal value HH (one or two hex digits)
              \cx    a control-x character

       The expanded result is single-quoted, as if the dollar sign had not been present.

       A double-quoted string preceded by a dollar sign ($) will cause the string to be translated according
       to  the  current  locale.   If  the current locale is C or POSIX, the dollar sign is ignored.  If the
       string is translated and replaced, the replacement is double-quoted.

PARAMETERS
       A parameter is an entity that stores values.  It can be a name, a number, or one of the special char-acters characters
       acters  listed below under Special Parameters.  A variable is a parameter denoted by a name.  A vari-able variable
       able has a value and zero or more attributes.  Attributes are assigned using the declare builtin com-mand command
       mand (see declare below in SHELL BUILTIN COMMANDS).

       A  parameter is set if it has been assigned a value.  The null string is a valid value.  Once a vari-able variable
       able is set, it may be unset only by using the unset builtin  command  (see  SHELL  BUILTIN  COMMANDS
       below).

       A variable may be assigned to by a statement of the form

              name=[value]

       If value is not given, the variable is assigned the null string.  All values undergo tilde expansion,
       parameter and variable expansion, command substitution, arithmetic expansion, and quote removal  (see
       EXPANSION  below).   If  the  variable  has  its integer attribute set, then value is evaluated as an
       arithmetic expression even if the $((...)) expansion is not used (see  Arithmetic  Expansion  below).
       Word  splitting is not performed, with the exception of "$@" as explained below under Special Parame-ters. Parameters.
       ters.  Pathname expansion is not performed.  Assignment statements may also appear  as  arguments  to
       the alias, declare, typeset, export, readonly, and local builtin commands.

       In the context where an assignment statement is assigning a value to a shell variable or array index,
       the += operator can be used to append to or add to the variable's previous value.  When += is applied
       to  a  variable  for  which  the  integer attribute has been set, value is evaluated as an arithmetic
       expression and added to the variable's current value, which is also evaluated.  When += is applied to
       an array variable using compound assignment (see Arrays below), the variable's value is not unset (as
       it is when using =), and new values are appended to the array  beginning  at  one  greater  than  the
       array's  maximum  index.  When applied to a string-valued variable, value is expanded and appended to
       the variable's value.

   Positional Parameters
       A positional parameter is a parameter denoted by one or more digits, other than the single  digit  0.
       Positional  parameters  are  assigned from the shell's arguments when it is invoked, and may be reas-signed reassigned
       signed using the set builtin command.  Positional parameters may not be assigned to  with  assignment
       statements.   The  positional  parameters  are temporarily replaced when a shell function is executed
       (see FUNCTIONS below).

       When a positional parameter consisting of more than a single digit is expanded, it must  be  enclosed
       in braces (see EXPANSION below).

   Special Parameters
       The  shell  treats several parameters specially.  These parameters may only be referenced; assignment
       to them is not allowed.
       *      Expands to the positional parameters, starting from one.  When  the  expansion  occurs  within
              double  quotes,  it expands to a single word with the value of each parameter separated by the
              first character of the IFS special variable.  That is,  "$*"  is  equivalent  to  "$1c$2c...",
              where c is the first character of the value of the IFS variable.  If IFS is unset, the parame-ters parameters
              ters are separated by spaces.  If IFS is null, the parameters are joined  without  intervening
              separators.
       @      Expands  to  the  positional  parameters, starting from one.  When the expansion occurs within
              double quotes, each parameter expands to a separate word.  That is, "$@" is equivalent to "$1"
              "$2"  ...   If  the  double-quoted  expansion occurs within a word, the expansion of the first
              parameter is joined with the beginning part of the original word, and  the  expansion  of  the
              last  parameter  is  joined  with the last part of the original word.  When there are no posi-tional positional
              tional parameters, "$@" and $@ expand to nothing (i.e., they are removed).
       #      Expands to the number of positional parameters in decimal.
       ?      Expands to the status of the most recently executed foreground pipeline.
       -      Expands to the current option flags as specified upon invocation, by the set builtin  command,
              or those set by the shell itself (such as the -i option).
       $      Expands to the process ID of the shell.  In a () subshell, it expands to the process ID of the
              current shell, not the subshell.
       !      Expands to the process ID of the most recently executed background (asynchronous) command.
       0      Expands to the name of the shell or shell script.  This is set at  shell  initialization.   If
              bash  is  invoked  with  a  file  of commands, $0 is set to the name of that file.  If bash is
              started with the -c option, then $0 is set to the first argument after the string to  be  exe-cuted, executed,
              cuted, if one is present.  Otherwise, it is set to the file name used to invoke bash, as given
              by argument zero.
       _      At shell startup, set to the absolute pathname used to invoke the shell or shell script  being
              executed  as  passed  in  the environment or argument list.  Subsequently, expands to the last
              argument to the previous command, after expansion.  Also set to  the  full  pathname  used  to
              invoke  each  command  executed  and placed in the environment exported to that command.  When
              checking mail, this parameter holds the name of the mail file currently being checked.

   Shell Variables
       The following variables are set by the shell:

       BASH   Expands to the full file name used to invoke this instance of bash.
       BASH_ARGC
              An array variable whose values are the number of parameters in each frame of the current  bash
              execution  call  stack.  The number of parameters to the current subroutine (shell function or
              script executed with . or source) is at the top of the stack.  When a subroutine is  executed,
              the  number of parameters passed is pushed onto BASH_ARGC.  The shell sets BASH_ARGC only when
              in extended debugging mode (see the description of the extdebug option to  the  shopt  builtin
              below)
       BASH_ARGV
              An  array  variable containing all of the parameters in the current bash execution call stack.
              The final parameter of the last subroutine call is at the top of the stack; the first  parame-ter parameter
              ter  of the initial call is at the bottom.  When a subroutine is executed, the parameters sup-plied supplied
              plied are pushed onto BASH_ARGV.  The shell sets BASH_ARGV only  when  in  extended  debugging
              mode (see the description of the extdebug option to the shopt builtin below)
       BASH_COMMAND
              The  command currently being executed or about to be executed, unless the shell is executing a
              command as the result of a trap, in which case it is the command executing at the time of  the
              trap.
       BASH_EXECUTION_STRING
              The command argument to the -c invocation option.
       BASH_LINENO
              An  array  variable  whose  members are the line numbers in source files corresponding to each
              member of FUNCNAME.  ${BASH_LINENO[$i]} is the line number in the source  file  where  ${FUNC-NAME[$ifP]} ${FUNCNAME[$ifP]}
              NAME[$ifP]} was called.  The corresponding source file name is ${BASH_SOURCE[$i]}.  Use LINENO
              to obtain the current line number.
       BASH_REMATCH
              An array variable whose members are assigned by the =~ binary operator to the  [[  conditional
              command.   The  element  with index 0 is the portion of the string matching the entire regular
              expression.  The element with index n is the portion of the string matching the nth  parenthe-sized parenthesized
              sized subexpression.  This variable is read-only.
       BASH_SOURCE
              An  array variable whose members are the source filenames corresponding to the elements in the
              FUNCNAME array variable.
       BASH_SUBSHELL
              Incremented by one each time a subshell or subshell environment is spawned.  The initial value
              is 0.
       BASH_VERSINFO
              A  readonly  array  variable whose members hold version information for this instance of bash.
              The values assigned to the array members are as follows:
              BASH_VERSINFO[0]        The major version number (the release).
              BASH_VERSINFO[1]        The minor version number (the version).
              BASH_VERSINFO[2]        The patch level.
              BASH_VERSINFO[3]        The build version.
              BASH_VERSINFO[4]        The release status (e.g., beta1).
              BASH_VERSINFO[5]        The value of MACHTYPE.

       BASH_VERSION
              Expands to a string describing the version of this instance of bash.

       COMP_CWORD
              An index into ${COMP_WORDS} of the word containing the current cursor position.  This variable
              is  available  only  in shell functions invoked by the programmable completion facilities (see
              Programmable Completion below).

       COMP_LINE
              The current command line.  This variable is available only in  shell  functions  and  external
              commands  invoked  by  the  programmable  completion  facilities  (see Programmable Completion
              below).

       COMP_POINT
              The index of the current cursor position relative to the beginning of the current command.  If
              the  current  cursor position is at the end of the current command, the value of this variable
              is equal to ${#COMP_LINE}.  This variable is available only in shell  functions  and  external
              commands  invoked  by  the  programmable  completion  facilities  (see Programmable Completion
              below).

       COMP_WORDBREAKS
              The set of characters that the Readline library treats as word separators when performing word
              completion.   If COMP_WORDBREAKS is unset, it loses its special properties, even if it is sub-sequently subsequently
              sequently reset.

       COMP_WORDS
              An array variable (see Arrays below) consisting of the individual words in the current command
              line.   The  words  are split on shell metacharacters as the shell parser would separate them.
              This variable is available only in shell functions  invoked  by  the  programmable  completion
              facilities (see Programmable Completion below).

       DIRSTACK
              An  array  variable (see Arrays below) containing the current contents of the directory stack.
              Directories appear in the stack in the order they are displayed by the dirs builtin.   Assign-ing Assigning
              ing  to members of this array variable may be used to modify directories already in the stack,
              but the pushd and popd builtins must be used to add and  remove  directories.   Assignment  to
              this  variable will not change the current directory.  If DIRSTACK is unset, it loses its spe-cial special
              cial properties, even if it is subsequently reset.

       EUID   Expands to the effective user ID of the current user,  initialized  at  shell  startup.   This
              variable is readonly.

       FUNCNAME
              An  array variable containing the names of all shell functions currently in the execution call
              stack.  The element with index 0 is the name of any currently-executing shell  function.   The
              bottom-most  element is "main".  This variable exists only when a shell function is executing.
              Assignments to FUNCNAME have no effect and return an error status.  If FUNCNAME is  unset,  it
              loses its special properties, even if it is subsequently reset.

       GROUPS An  array  variable  containing  the  list  of  groups  of which the current user is a member.
              Assignments to GROUPS have no effect and return an error status.  If GROUPS is unset, it loses
              its special properties, even if it is subsequently reset.

       HISTCMD
              The  history  number,  or  index  in  the history list, of the current command.  If HISTCMD is
              unset, it loses its special properties, even if it is subsequently reset.

       HOSTNAME
              Automatically set to the name of the current host.

       HOSTTYPE
              Automatically set to a string that uniquely describes the type of machine  on  which  bash  is
              executing.  The default is system-dependent.

       LINENO Each  time  this  parameter is referenced, the shell substitutes a decimal number representing
              the current sequential line number (starting with 1) within a script or function.  When not in
              a  script or function, the value substituted is not guaranteed to be meaningful.  If LINENO is
              unset, it loses its special properties, even if it is subsequently reset.

       MACHTYPE
              Automatically set to a string that fully describes the system type on which bash is executing,
              in the standard GNU cpu-company-system format.  The default is system-dependent.

       OLDPWD The previous working directory as set by the cd command.

       OPTARG The  value  of  the  last  option argument processed by the getopts builtin command (see SHELL
              BUILTIN COMMANDS below).

       OPTIND The index of the next argument to be processed by  the  getopts  builtin  command  (see  SHELL
              BUILTIN COMMANDS below).

       OSTYPE Automatically  set to a string that describes the operating system on which bash is executing.
              The default is system-dependent.

       PIPESTATUS
              An array variable (see Arrays below) containing a list of exit status  values  from  the  pro-cesses processes
              cesses in the most-recently-executed foreground pipeline (which may contain only a single com-mand). command).
              mand).

       PPID   The process ID of the shell's parent.  This variable is readonly.

       PWD    The current working directory as set by the cd command.

       RANDOM Each time this parameter is referenced, a random integer between 0  and  32767  is  generated.
              The  sequence  of random numbers may be initialized by assigning a value to RANDOM.  If RANDOM
              is unset, it loses its special properties, even if it is subsequently reset.

       REPLY  Set to the line of input read by the read builtin command when no arguments are supplied.

       SECONDS
              Each time this parameter is referenced, the  number  of  seconds  since  shell  invocation  is
              returned.  If a value is assigned to SECONDS, the value returned upon subsequent references is
              the number of seconds since the assignment plus the value assigned.  If SECONDS is  unset,  it
              loses its special properties, even if it is subsequently reset.

       SHELLOPTS
              A  colon-separated  list  of enabled shell options.  Each word in the list is a valid argument
              for the -o option to the set builtin command (see SHELL BUILTIN COMMANDS below).  The  options
              appearing  in  SHELLOPTS are those reported as on by set -o.  If this variable is in the envi-ronment environment
              ronment when bash starts up, each shell option in the list will be enabled before reading  any
              startup files.  This variable is read-only.

       SHLVL  Incremented by one each time an instance of bash is started.

       UID    Expands  to  the  user ID of the current user, initialized at shell startup.  This variable is
              readonly.

       The following variables are used by the shell.  In some cases, bash assigns  a  default  value  to  a
       variable; these cases are noted below.

       BASH_ENV
              If  this parameter is set when bash is executing a shell script, its value is interpreted as a
              filename containing commands to initialize the shell, as in ~/.bashrc.  The value of  BASH_ENV
              is  subjected  to  parameter  expansion, command substitution, and arithmetic expansion before
              being interpreted as a file name.  PATH is not used to search for the resultant file name.
       CDPATH The search path for the cd command.  This is a colon-separated list of  directories  in  which
              the  shell  looks  for destination directories specified by the cd command.  A sample value is
              ".:~:/usr".
       COLUMNS
              Used by the select builtin command to determine the terminal  width  when  printing  selection
              lists.  Automatically set upon receipt of a SIGWINCH.
       COMPREPLY
              An array variable from which bash reads the possible completions generated by a shell function
              invoked by the programmable completion facility (see Programmable Completion below).
       EMACS  If bash finds this variable in the environment when  the  shell  starts  with  value  "t",  it
              assumes that the shell is running in an emacs shell buffer and disables line editing.
       FCEDIT The default editor for the fc builtin command.
       FIGNORE
              A colon-separated list of suffixes to ignore when performing filename completion (see READLINE
              below).  A filename whose suffix matches one of the entries in FIGNORE is  excluded  from  the
              list of matched filenames.  A sample value is ".o:~".
       GLOBIGNORE
              A  colon-separated  list  of  patterns defining the set of filenames to be ignored by pathname
              expansion.  If a filename matched by a pathname expansion pattern also matches one of the pat-terns patterns
              terns in GLOBIGNORE, it is removed from the list of matches.
       HISTCONTROL
              A  colon-separated  list of values controlling how commands are saved on the history list.  If
              the list of values includes ignorespace, lines which begin with  a  space  character  are  not
              saved  in  the history list.  A value of ignoredups causes lines matching the previous history
              entry to not be saved.  A value of ignoreboth is shorthand for ignorespace and ignoredups.   A
              value  of erasedups causes all previous lines matching the current line to be removed from the
              history list before that line is saved.  Any value not in the above list is ignored.  If HIST-CONTROL HISTCONTROL
              CONTROL  is  unset,  or does not include a valid value, all lines read by the shell parser are
              saved on the history list, subject to the value of  HISTIGNORE.   The  second  and  subsequent
              lines of a multi-line compound command are not tested, and are added to the history regardless
              of the value of HISTCONTROL.
       HISTFILE
              The name of the file in which command history is saved (see HISTORY below).  The default value
              is  ~/.bash_history.   If  unset,  the  command history is not saved when an interactive shell
              exits.
       HISTFILESIZE
              The maximum number of lines contained in the history file.  When this variable is  assigned  a
              value, the history file is truncated, if necessary, by removing the oldest entries, to contain
              no more than that number of lines.  The default value is 500.  The history file is also  trun-cated truncated
              cated to this size after writing it when an interactive shell exits.
       HISTIGNORE
              A  colon-separated  list of patterns used to decide which command lines should be saved on the
              history list.  Each pattern is anchored at the beginning of the line and must match  the  com-plete complete
              plete  line  (no implicit `*' is appended).  Each pattern is tested against the line after the
              checks specified by HISTCONTROL are applied.  In addition to the normal shell pattern matching
              characters,  `&' matches the previous history line.  `&' may be escaped using a backslash; the
              backslash is removed before attempting a match.  The second and subsequent lines of  a  multi-line multiline
              line  compound command are not tested, and are added to the history regardless of the value of
              HISTIGNORE.
       HISTSIZE
              The number of commands to remember in the command history (see HISTORY  below).   The  default
              value is 500.
       HISTTIMEFORMAT
              If  this variable is set and not null, its value is used as a format string for strftime(3) to
              print the time stamp associated with each history entry displayed by the history builtin.   If
              this  variable  is  set,  time stamps are written to the history file so they may be preserved
              across shell sessions.
       HOME   The home directory of the current user; the default argument for the cd builtin command.   The
              value of this variable is also used when performing tilde expansion.
       HOSTFILE
              Contains  the  name  of  a  file in the same format as /etc/hosts that should be read when the
              shell needs to complete a hostname.  The list of possible hostname completions may be  changed
              while  the shell is running; the next time hostname completion is attempted after the value is
              changed, bash adds the contents of the new file to the existing list.  If HOSTFILE is set, but
              has no value, bash attempts to read /etc/hosts to obtain the list of possible hostname comple-tions. completions.
              tions.  When HOSTFILE is unset, the hostname list is cleared.
       IFS    The Internal Field Separator that is used for word splitting  after  expansion  and  to  split
              lines  into  words  with  the  read builtin command.  The default value is ``<space><tab><new-
              line>''.
       IGNOREEOF
              Controls the action of an interactive shell on receipt of an EOF character as the sole  input.
              If set, the value is the number of consecutive EOF characters which must be typed as the first
              characters on an input line before bash exits.  If the variable exists but  does  not  have  a
              numeric  value, or has no value, the default value is 10.  If it does not exist, EOF signifies
              the end of input to the shell.
       INPUTRC
              The filename for the readline startup file, overriding the default of ~/.inputrc (see READLINE
              below).
       LANG   Used  to determine the locale category for any category not specifically selected with a vari-able variable
              able starting with LC_.
       LC_ALL This variable overrides the value of LANG and any other LC_ variable specifying a locale cate-gory. category.
              gory.
       LC_COLLATE
              This  variable determines the collation order used when sorting the results of pathname expan-sion, expansion,
              sion, and determines the behavior of range expressions,  equivalence  classes,  and  collating
              sequences within pathname expansion and pattern matching.
       LC_CTYPE
              This  variable  determines  the  interpretation  of  characters  and the behavior of character
              classes within pathname expansion and pattern matching.
       LC_MESSAGES
              This variable determines the locale used to translate double-quoted strings preceded by a $.
       LC_NUMERIC
              This variable determines the locale category used for number formatting.
       LINES  Used by the select builtin command to determine  the  column  length  for  printing  selection
              lists.  Automatically set upon receipt of a SIGWINCH.
       MAIL   If this parameter is set to a file name and the MAILPATH variable is not set, bash informs the
              user of the arrival of mail in the specified file.
       MAILCHECK
              Specifies how often (in seconds) bash checks for mail.  The default is 60 seconds.  When it is
              time to check for mail, the shell does so before displaying the primary prompt.  If this vari-able variable
              able is unset, or set to a value that is not a number greater than or equal to zero, the shell
              disables mail checking.
       MAILPATH
              A  colon-separated  list of file names to be checked for mail.  The message to be printed when
              mail arrives in a particular file may be specified by separating the file name from  the  mes-sage message
              sage  with a `?'.  When used in the text of the message, $_ expands to the name of the current
              mailfile.  Example:
              MAILPATH='/var/mail/bfox?"You have mail":~/shell-mail?"$_ has mail!"'
              Bash supplies a default value for this variable, but the location of the user mail files  that
              it uses is system dependent (e.g., /var/mail/$USER).
       OPTERR If  set  to the value 1, bash displays error messages generated by the getopts builtin command
              (see SHELL BUILTIN COMMANDS below).  OPTERR is initialized to 1 each time the shell is invoked
              or a shell script is executed.
       PATH   The  search path for commands.  It is a colon-separated list of directories in which the shell
              looks for commands (see COMMAND EXECUTION below).  A zero-length (null) directory name in  the
              value  of PATH indicates the current directory.  A null directory name may appear as two adja-cent adjacent
              cent colons, or as an initial or trailing colon.  The default path is system-dependent, and is
              set     by     the    administrator    who    installs    bash.     A    common    value    is
              ``/usr/gnu/bin:/usr/local/bin:/usr/ucb:/bin:/usr/bin''.
       POSIXLY_CORRECT
              If this variable is in the environment when bash starts, the shell enters  posix  mode  before
              reading  the  startup  files, as if the --posix invocation option had been supplied.  If it is
              set while the shell is running, bash enables posix mode, as if the command set  -o  posix  had
              been executed.
       PROMPT_COMMAND
              If set, the value is executed as a command prior to issuing each primary prompt.
       PS1    The  value  of this parameter is expanded (see PROMPTING below) and used as the primary prompt
              string.  The default value is ``\s-\v\$ ''.
       PS2    The value of this parameter is expanded as with PS1 and used as the secondary  prompt  string.
              The default is ``> ''.
       PS3    The  value  of  this parameter is used as the prompt for the select command (see SHELL GRAMMAR
              above).
       PS4    The value of this parameter is expanded as with PS1 and the value is printed before each  com-mand command
              mand bash displays during an execution trace.  The first character of PS4 is replicated multi-ple multiple
              ple times, as necessary, to indicate multiple levels of indirection.  The default is ``+ ''.
       SHELL  The full pathname to the shell is kept in this environment variable.  If it is  not  set  when
              the shell starts, bash assigns to it the full pathname of the current user's login shell.
       TIMEFORMAT
              The  value  of this parameter is used as a format string specifying how the timing information
              for pipelines prefixed with the time reserved word  should  be  displayed.   The  %  character
              introduces  an  escape  sequence  that  is expanded to a time value or other information.  The
              escape sequences and their meanings are as follows; the braces denote optional portions.
              %%        A literal %.
              %[p][l]R  The elapsed time in seconds.
              %[p][l]U  The number of CPU seconds spent in user mode.
              %[p][l]S  The number of CPU seconds spent in system mode.
              %P        The CPU percentage, computed as (%U + %S) / %R.

              The optional p is a digit specifying the precision, the number of fractional  digits  after  a
              decimal  point.  A value of 0 causes no decimal point or fraction to be output.  At most three
              places after the decimal point may be specified; values of p greater than 3 are changed to  3.
              If p is not specified, the value 3 is used.

              The optional l specifies a longer format, including minutes, of the form MMmSS.FFs.  The value
              of p determines whether or not the fraction is included.

              If   this   variable   is   not   set,   bash    acts    as    if    it    had    the    value
              $'\nreal\t%3lR\nuser\t%3lU\nsys%3lS'.   If  the  value  is null, no timing information is dis-played. displayed.
              played.  A trailing newline is added when the format string is displayed.

       TMOUT  If set to a value greater than zero, TMOUT is treated as the  default  timeout  for  the  read
              builtin.   The  select  command  terminates  if input does not arrive after TMOUT seconds when
              input is coming from a terminal.  In an interactive shell, the value  is  interpreted  as  the
              number  of  seconds to wait for input after issuing the primary prompt.  Bash terminates after
              waiting for that number of seconds if input does not arrive.

       TMPDIR If set, Bash uses its value as the name of a directory in which Bash creates  temporary  files
              for the shell's use.

       auto_resume
              This  variable  controls how the shell interacts with the user and job control.  If this vari-able variable
              able is set, single word simple commands without redirections are treated  as  candidates  for
              resumption  of  an existing stopped job.  There is no ambiguity allowed; if there is more than
              one job beginning with the string typed, the job most recently accessed is selected.  The name
              of  a stopped job, in this context, is the command line used to start it.  If set to the value
              exact, the string supplied must match the name of a stopped job exactly; if set to  substring,
              the  string  supplied  needs to match a substring of the name of a stopped job.  The substring
              value provides functionality analogous to the %?  job identifier (see JOB CONTROL below).   If
              set  to  any  other  value, the supplied string must be a prefix of a stopped job's name; this
              provides functionality analogous to the %string job identifier.

       histchars
              The two or three characters which control history  expansion  and  tokenization  (see  HISTORY
              EXPANSION below).  The first character is the history expansion character, the character which
              signals the start of a history expansion, normally `!'.  The second  character  is  the  quick
              substitution  character,  which  is  used  as  shorthand  for  re-running the previous command
              entered, substituting one string for another  in  the  command.   The  default  is  `^'.   The
              optional  third character is the character which indicates that the remainder of the line is a
              comment when found as the first character of a word, normally `#'.  The history comment  char-acter character
              acter  causes history substitution to be skipped for the remaining words on the line.  It does
              not necessarily cause the shell parser to treat the rest of the line as a comment.

   Arrays
       Bash provides one-dimensional array variables.  Any variable may be used as  an  array;  the  declare
       builtin will explicitly declare an array.  There is no maximum limit on the size of an array, nor any
       requirement that members be indexed or assigned contiguously.  Arrays are indexed using integers  and
       are zero-based.

       An  array  is  created  automatically  if  any  variable  is  assigned  to using the syntax name[sub-script]=value. name[subscript]=value.
       script]=value.  The subscript is treated as an arithmetic expression that must evaluate to  a  number
       greater  than  or  equal  to  zero.   To  explicitly declare an array, use declare -a name (see SHELL
       BUILTIN COMMANDS below).  declare -a name[subscript] is also  accepted;  the  subscript  is  ignored.
       Attributes  may  be  specified  for  an array variable using the declare and readonly builtins.  Each
       attribute applies to all members of an array.

       Arrays are assigned to using compound assignments of the form name=(value1 ...  valuen),  where  each
       value is of the form [subscript]=string.  Only string is required.  If the optional brackets and sub-script subscript
       script are supplied, that index is assigned to; otherwise the index of the element  assigned  is  the
       last  index  assigned  to  by  the statement plus one.  Indexing starts at zero.  This syntax is also
       accepted by the declare builtin.  Individual array elements may be assigned to  using  the  name[sub-script]=value name[subscript]=value
       script]=value syntax introduced above.

       Any element of an array may be referenced using ${name[subscript]}.  The braces are required to avoid
       conflicts with pathname expansion.  If subscript is @ or *, the word expands to all members of  name.
       These  subscripts  differ  only  when  the word appears within double quotes.  If the word is double-quoted, doublequoted,
       quoted, ${name[*]} expands to a single word with the value of each  array  member  separated  by  the
       first  character  of the IFS special variable, and ${name[@]} expands each element of name to a sepa-rate separate
       rate word.  When there are no array members, ${name[@]} expands to  nothing.   If  the  double-quoted
       expansion  occurs  within  a  word, the expansion of the first parameter is joined with the beginning
       part of the original word, and the expansion of the last parameter is joined with the  last  part  of
       the original word.  This is analogous to the expansion of the special parameters * and @ (see Special
       Parameters above).  ${#name[subscript]} expands to the length of ${name[subscript]}.  If subscript is
       *  or @, the expansion is the number of elements in the array.  Referencing an array variable without
       a subscript is equivalent to referencing element zero.

       The unset builtin is used to destroy arrays.  unset name[subscript] destroys  the  array  element  at
       index  subscript.   Care  must be taken to avoid unwanted side effects caused by filename generation.
       unset name, where name is an array, or unset name[subscript], where subscript is * or @, removes  the
       entire array.

       The  declare,  local,  and  readonly  builtins each accept a -a option to specify an array.  The read
       builtin accepts a -a option to assign a list of words read from the standard input to an array.   The
       set  and declare builtins display array values in a way that allows them to be reused as assignments.

EXPANSION
       Expansion is performed on the command line after it has been split into words.  There are seven kinds
       of  expansion  performed: brace expansion, tilde expansion, parameter and variable expansion, command
       substitution, arithmetic expansion, word splitting, and pathname expansion.

       The order of expansions is: brace expansion, tilde  expansion,  parameter,  variable  and  arithmetic
       expansion  and  command  substitution (done in a left-to-right fashion), word splitting, and pathname
       expansion.

       On systems that can support it, there is an additional expansion available: process substitution.

       Only brace expansion, word splitting, and pathname expansion can change the number of  words  of  the
       expansion;  other  expansions expand a single word to a single word.  The only exceptions to this are
       the expansions of "$@" and "${name[@]}" as explained above (see PARAMETERS).

   Brace Expansion
       Brace expansion is a mechanism by which arbitrary strings may be generated.  This mechanism is  simi-lar similar
       lar to pathname expansion, but the filenames generated need not exist.  Patterns to be brace expanded
       take the form of an optional preamble, followed by either a series of comma-separated  strings  or  a
       sequence  expression  between  a pair of braces, followed by an optional postscript.  The preamble is
       prefixed to each string contained within the braces, and the postscript  is  then  appended  to  each
       resulting string, expanding left to right.

       Brace  expansions  may  be nested.  The results of each expanded string are not sorted; left to right
       order is preserved.  For example, a{d,c,b}e expands into `ade ace abe'.

       A sequence expression takes the form {x..y}, where x and y are either integers or single  characters.
       When  integers  are supplied, the expression expands to each number between x and y, inclusive.  When
       characters are supplied, the expression expands to each character lexicographically between x and  y,
       inclusive.  Note that both x and y must be of the same type.

       Brace  expansion is performed before any other expansions, and any characters special to other expan-sions expansions
       sions are preserved in the result.  It is strictly textual.  Bash does not apply any syntactic inter-pretation interpretation
       pretation to the context of the expansion or the text between the braces.

       A correctly-formed brace expansion must contain unquoted opening and closing braces, and at least one
       unquoted comma or a valid sequence expression.   Any  incorrectly  formed  brace  expansion  is  left
       unchanged.   A  { or , may be quoted with a backslash to prevent its being considered part of a brace
       expression.  To avoid conflicts with parameter expansion, the string ${ is  not  considered  eligible
       for brace expansion.

       This  construct  is typically used as shorthand when the common prefix of the strings to be generated
       is longer than in the above example:

              mkdir /usr/local/src/bash/{old,new,dist,bugs}
       or
              chown root /usr/{ucb/{ex,edit},lib/{ex?.?*,how_ex}}

       Brace expansion introduces a slight incompatibility with historical versions  of  sh.   sh  does  not
       treat  opening  or closing braces specially when they appear as part of a word, and preserves them in
       the output.  Bash removes braces from words as a consequence of brace expansion.  For example, a word
       entered to sh as file{1,2} appears identically in the output.  The same word is output as file1 file2
       after expansion by bash.  If strict compatibility with sh is desired, start bash with the  +B  option
       or  disable brace expansion with the +B option to the set command (see SHELL BUILTIN COMMANDS below).

   Tilde Expansion
       If a word begins with an unquoted tilde character (`~'), all of the characters  preceding  the  first
       unquoted  slash (or all characters, if there is no unquoted slash) are considered a tilde-prefix.  If
       none of the characters in the tilde-prefix are quoted, the characters in the  tilde-prefix  following
       the  tilde are treated as a possible login name.  If this login name is the null string, the tilde is
       replaced with the value of the shell parameter HOME.  If HOME is unset, the  home  directory  of  the
       user  executing  the  shell is substituted instead.  Otherwise, the tilde-prefix is replaced with the
       home directory associated with the specified login name.

       If the tilde-prefix is a `~+', the value of the shell variable PWD replaces the tilde-prefix.  If the
       tilde-prefix is a `~-', the value of the shell variable OLDPWD, if it is set, is substituted.  If the
       characters following the tilde in the tilde-prefix consist of a number N, optionally  prefixed  by  a
       `+'  or  a `-', the tilde-prefix is replaced with the corresponding element from the directory stack,
       as it would be displayed by the dirs builtin invoked with the tilde-prefix as an  argument.   If  the
       characters  following the tilde in the tilde-prefix consist of a number without a leading `+' or `-',
       `+' is assumed.

       If the login name is invalid, or the tilde expansion fails, the word is unchanged.

       Each variable assignment is checked for unquoted tilde-prefixes immediately  following  a  :  or  the
       first  =.   In  these cases, tilde expansion is also performed.  Consequently, one may use file names
       with tildes in assignments to PATH, MAILPATH, and CDPATH, and the shell assigns the expanded value.

   Parameter Expansion
       The `$' character introduces parameter expansion, command substitution, or arithmetic expansion.  The
       parameter  name  or  symbol to be expanded may be enclosed in braces, which are optional but serve to
       protect the variable to be expanded from characters immediately following it which  could  be  inter-preted interpreted
       preted as part of the name.

       When braces are used, the matching ending brace is the first `}' not escaped by a backslash or within
       a quoted string, and not within an embedded arithmetic expansion, command substitution, or  parameter
       expansion.

       ${parameter}
              The value of parameter is substituted.  The braces are required when parameter is a positional
              parameter with more than one digit, or when parameter is followed by a character which is  not
              to be interpreted as part of its name.

       If  the  first  character  of  parameter  is an exclamation point, a level of variable indirection is
       introduced.  Bash uses the value of the variable formed from the rest of parameter as the name of the
       variable;  this  variable  is  then  expanded and that value is used in the rest of the substitution,
       rather than the value of parameter itself.  This is known as indirect expansion.  The  exceptions  to
       this  are  the expansions of ${!prefix*} and ${!name[@]} described below.  The exclamation point must
       immediately follow the left brace in order to introduce indirection.

       In each of the cases below, word is subject to tilde expansion, parameter expansion, command  substi-tution, substitution,
       tution,  and arithmetic expansion.  When not performing substring expansion, bash tests for a parame-ter parameter
       ter that is unset or null; omitting the colon results in a test only for a parameter that is unset.

       ${parameter:-word}
              Use Default Values.  If parameter is unset or null, the  expansion  of  word  is  substituted.
              Otherwise, the value of parameter is substituted.
       ${parameter:=word}
              Assign  Default  Values.   If parameter is unset or null, the expansion of word is assigned to
              parameter.  The value of parameter is then substituted.   Positional  parameters  and  special
              parameters may not be assigned to in this way.
       ${parameter:?word}
              Display  Error  if  Null or Unset.  If parameter is null or unset, the expansion of word (or a
              message to that effect if word is not present) is written to the standard error and the shell,
              if it is not interactive, exits.  Otherwise, the value of parameter is substituted.
       ${parameter:+word}
              Use  Alternate  Value.   If  parameter is null or unset, nothing is substituted, otherwise the
              expansion of word is substituted.
       ${parameter:offset}
       ${parameter:offset:length}
              Substring Expansion.  Expands to up to length characters of parameter starting at the  charac-ter character
              ter specified by offset.  If length is omitted, expands to the substring of parameter starting
              at the character specified by offset.  length  and  offset  are  arithmetic  expressions  (see
              ARITHMETIC EVALUATION below).  length must evaluate to a number greater than or equal to zero.
              If offset evaluates to a number less than zero, the value is used as an offset from the end of
              the  value of parameter.  If parameter is @, the result is length positional parameters begin-ning beginning
              ning at offset.  If parameter is an array name indexed by @ or *, the  result  is  the  length
              members of the array beginning with ${parameter[offset]}.  A negative offset is taken relative
              to one greater than the maximum index of the specified array.  Note  that  a  negative  offset
              must  be  separated  from  the colon by at least one space to avoid being confused with the :-expansion. :expansion.
              expansion.  Substring indexing is zero-based unless the positional  parameters  are  used,  in
              which case the indexing starts at 1.

       ${!prefix*}
       ${!prefix@}
              Expands  to the names of variables whose names begin with prefix, separated by the first char-acter character
              acter of the IFS special variable.

       ${!name[@]}
       ${!name[*]}
              If name is an array variable, expands to the list of array indices (keys)  assigned  in  name.
              If  name  is not an array, expands to 0 if name is set and null otherwise.  When @ is used and
              the expansion appears within double quotes, each key expands to a separate word.

       ${#parameter}
              The length in characters of the value of parameter is substituted.  If parameter is  *  or  @,
              the  value  substituted is the number of positional parameters.  If parameter is an array name
              subscripted by * or @, the value substituted is the number of elements in the array.

       ${parameter#word}
       ${parameter##word}
              The word is expanded to produce a pattern just as  in  pathname  expansion.   If  the  pattern
              matches  the  beginning  of  the  value  of parameter, then the result of the expansion is the
              expanded value of parameter with the shortest matching pattern (the ``#'' case) or the longest
              matching pattern (the ``##'' case) deleted.  If parameter is @ or *, the pattern removal oper-ation operation
              ation is applied to each positional parameter in turn, and  the  expansion  is  the  resultant
              list.   If  parameter is an array variable subscripted with @ or *, the pattern removal opera-tion operation
              tion is applied to each member of the array in turn, and the expansion is the resultant  list.

       ${parameter%word}
       ${parameter%%word}
              The  word  is  expanded  to  produce  a pattern just as in pathname expansion.  If the pattern
              matches a trailing portion of the expanded value of parameter, then the result of  the  expan-sion expansion
              sion is the expanded value of parameter with the shortest matching pattern (the ``%'' case) or
              the longest matching pattern (the ``%%'' case) deleted.  If parameter is @ or *,  the  pattern
              removal  operation  is  applied to each positional parameter in turn, and the expansion is the
              resultant list.  If parameter is an array variable  subscripted  with  @  or  *,  the  pattern
              removal  operation  is  applied  to each member of the array in turn, and the expansion is the
              resultant list.

       ${parameter/pattern/string}
              The pattern is expanded to produce a pattern just as  in  pathname  expansion.   Parameter  is
              expanded and the longest match of pattern against its value is replaced with string.  If Ipat-tern Ipattern
              tern begins with /, all matches of pattern are replaced with string.  Normally only the  first
              match  is  replaced.  If pattern begins with #, it must match at the beginning of the expanded
              value of parameter.  If pattern begins with %, it must match at the end of the expanded  value
              of  parameter.   If string is null, matches of pattern are deleted and the / following pattern
              may be omitted.  If parameter is @ or *, the substitution operation is applied to  each  posi-tional positional
              tional  parameter  in turn, and the expansion is the resultant list.  If parameter is an array
              variable subscripted with @ or *, the substitution operation is applied to each member of  the
              array in turn, and the expansion is the resultant list.

   Command Substitution
       Command  substitution  allows  the  output  of  a command to replace the command name.  There are two
       forms:


              $(command)
       or
              `command`

       Bash performs the expansion by executing command and replacing  the  command  substitution  with  the
       standard  output  of  the  command,  with  any  trailing newlines deleted.  Embedded newlines are not
       deleted, but they may be removed during word splitting.  The command substitution $(cat file) can  be
       replaced by the equivalent but faster $(< file).

       When  the  old-style  backquote  form  of substitution is used, backslash retains its literal meaning
       except when followed by $, `, or \.  The first backquote not preceded by a backslash  terminates  the
       command substitution.  When using the $(command) form, all characters between the parentheses make up
       the command; none are treated specially.

       Command substitutions may be nested.  To nest when using the backquoted form, escape the inner  back-
       quotes with backslashes.

       If  the substitution appears within double quotes, word splitting and pathname expansion are not per-formed performed
       formed on the results.

   Arithmetic Expansion
       Arithmetic expansion allows the evaluation of an arithmetic expression and the  substitution  of  the
       result.  The format for arithmetic expansion is:

              $((expression))

       The expression is treated as if it were within double quotes, but a double quote inside the parenthe-ses parentheses
       ses is not treated specially.  All tokens in  the  expression  undergo  parameter  expansion,  string
       expansion, command substitution, and quote removal.  Arithmetic expansions may be nested.

       The  evaluation  is  performed  according  to the rules listed below under ARITHMETIC EVALUATION.  If
       expression is invalid, bash prints a message indicating failure and no substitution occurs.

   Process Substitution
       Process substitution is supported on systems that support named pipes (FIFOs) or the  /dev/fd  method
       of  naming  open  files.   It takes the form of <(list) or >(list).  The process list is run with its
       input or output connected to a FIFO or some file in /dev/fd.  The name of this file is passed  as  an
       argument to the current command as the result of the expansion.  If the >(list) form is used, writing
       to the file will provide input for list.  If the <(list) form is used, the file passed as an argument
       should be read to obtain the output of list.

       When  available,  process substitution is performed simultaneously with parameter and variable expan-
       sion, command substitution, and arithmetic expansion.

   Word Splitting
       The shell scans the results of parameter expansion, command substitution,  and  arithmetic  expansion
       that did not occur within double quotes for word splitting.

       The shell treats each character of IFS as a delimiter, and splits the results of the other expansions
       into words on these characters.  If IFS is unset, or its value is exactly <space><tab><newline>,  the
       default,  then any sequence of IFS characters serves to delimit words.  If IFS has a value other than
       the default, then sequences of the whitespace characters space and tab are ignored at  the  beginning
       and  end  of  the word, as long as the whitespace character is in the value of IFS (an IFS whitespace
       character).  Any character in IFS that is not IFS whitespace, along with any adjacent IFS  whitespace
       characters,  delimits  a  field.  A sequence of IFS whitespace characters is also treated as a delim-iter. delimiter.
       iter.  If the value of IFS is null, no word splitting occurs.

       Explicit null arguments ("" or '') are retained.  Unquoted implicit null  arguments,  resulting  from
       the  expansion  of  parameters  that  have  no  values, are removed.  If a parameter with no value is
       expanded within double quotes, a null argument results and is retained.

       Note that if no expansion occurs, no splitting is performed.

   Pathname Expansion
       After word splitting, unless the -f option has been set, bash scans each word for the  characters  *,
       ?,  and  [.  If one of these characters appears, then the word is regarded as a pattern, and replaced
       with an alphabetically sorted list of file names matching the pattern.  If no matching file names are
       found, and the shell option nullglob is disabled, the word is left unchanged.  If the nullglob option
       is set, and no matches are found, the word is removed.  If the failglob shell option is set,  and  no
       matches  are found, an error message is printed and the command is not executed.  If the shell option
       nocaseglob is enabled, the match is performed without regard to the case  of  alphabetic  characters.
       When a pattern is used for pathname expansion, the character ``.''  at the start of a name or immedi-ately immediately
       ately following a slash must be matched explicitly, unless the shell option  dotglob  is  set.   When
       matching  a  pathname,  the  slash  character must always be matched explicitly.  In other cases, the
       ``.''  character is not treated specially.  See the description of shopt below  under  SHELL  BUILTIN
       COMMANDS for a description of the nocaseglob, nullglob, failglob, and dotglob shell options.

       The  GLOBIGNORE  shell variable may be used to restrict the set of file names matching a pattern.  If
       GLOBIGNORE is set, each matching file name that also matches one of the  patterns  in  GLOBIGNORE  is
       removed  from the list of matches.  The file names ``.''  and ``..''  are always ignored when GLOBIG-NORE GLOBIGNORE
       NORE is set and not null.  However, setting GLOBIGNORE to a non-null value has the effect of enabling
       the dotglob shell option, so all other file names beginning with a ``.''  will match.  To get the old
       behavior of ignoring file names beginning with a ``.'', make ``.*''  one of the patterns  in  GLOBIG-NORE. GLOBIGNORE.
       NORE.  The dotglob option is disabled when GLOBIGNORE is unset.

       Pattern Matching

       Any  character  that appears in a pattern, other than the special pattern characters described below,
       matches itself.  The NUL character may not occur in a pattern.  A  backslash  escapes  the  following
       character; the escaping backslash is discarded when matching.  The special pattern characters must be
       quoted if they are to be matched literally.

       The special pattern characters have the following meanings:

       *      Matches any string, including the null string.
       ?      Matches any single character.
       [...]  Matches any one of the enclosed characters.  A  pair  of  characters  separated  by  a  hyphen
              denotes  a range expression; any character that sorts between those two characters, inclusive,
              using the current locale's collating sequence and character set, is  matched.   If  the  first
              character  following  the  [  is  a !  or a ^ then any character not enclosed is matched.  The
              sorting order of characters in range expressions is determined by the current locale  and  the
              value  of  the  LC_COLLATE  shell variable, if set.  A - may be matched by including it as the
              first or last character in the set.  A ] may be matched by including it as the first character
              in the set.

              Within  [ and ], character classes can be specified using the syntax [:class:], where class is
              one of the following classes defined in the POSIX standard:
              alnum alpha ascii blank cntrl digit graph lower print punct space upper word xdigit
              A character class matches any character belonging to that class.   The  word  character  class
              matches letters, digits, and the character _.

              Within  [  and  ], an equivalence class can be specified using the syntax [=c=], which matches
              all characters with the same collation weight (as defined by the current locale) as the  char-acter character
              acter c.

              Within [ and ], the syntax [.symbol.] matches the collating symbol symbol.

       If  the  extglob  shell  option is enabled using the shopt builtin, several extended pattern matching
       operators are recognized.  In the following description, a pattern-list is a list of one or more pat-terns patterns
       terns separated by a |.  Composite patterns may be formed using one or more of the following sub-pat-terns: sub-patterns:
       terns:

              ?(pattern-list)
                     Matches zero or one occurrence of the given patterns
              *(pattern-list)
                     Matches zero or more occurrences of the given patterns
              +(pattern-list)
                     Matches one or more occurrences of the given patterns
              @(pattern-list)
                     Matches one of the given patterns
              !(pattern-list)
                     Matches anything except one of the given patterns

   Quote Removal
       After the preceding expansions, all unquoted occurrences of the characters \, ', and " that  did  not
       result from one of the above expansions are removed.

REDIRECTION
       Before  a command is executed, its input and output may be redirected using a special notation inter-preted interpreted
       preted by the shell.  Redirection may also be used to open and close files for the current shell exe-cution execution
       cution environment.  The following redirection operators may precede or appear anywhere within a sim-ple simple
       ple command or may follow a command.  Redirections are processed in the order they appear, from  left
       to right.

       In  the  following descriptions, if the file descriptor number is omitted, and the first character of
       the redirection operator is <, the redirection refers to the standard input (file descriptor 0).   If
       the  first  character of the redirection operator is >, the redirection refers to the standard output
       (file descriptor 1).

       The word following the redirection operator in the following descriptions, unless otherwise noted, is
       subjected  to brace expansion, tilde expansion, parameter expansion, command substitution, arithmetic
       expansion, quote removal, pathname expansion, and word splitting.  If it expands  to  more  than  one
       word, bash reports an error.

       Note that the order of redirections is significant.  For example, the command

              ls > dirlist 2>&1

       directs both standard output and standard error to the file dirlist, while the command

              ls 2>&1 > dirlist

       directs  only the standard output to file dirlist, because the standard error was duplicated as stan-dard standard
       dard output before the standard output was redirected to dirlist.

       Bash handles several filenames specially when they are used in redirections, as described in the fol-lowing following
       lowing table:

              /dev/fd/fd
                     If fd is a valid integer, file descriptor fd is duplicated.
              /dev/stdin
                     File descriptor 0 is duplicated.
              /dev/stdout
                     File descriptor 1 is duplicated.
              /dev/stderr
                     File descriptor 2 is duplicated.
              /dev/tcp/host/port
                     If  host is a valid hostname or Internet address, and port is an integer port number or
                     service name, bash attempts to open a TCP connection to the corresponding socket.
              /dev/udp/host/port
                     If host is a valid hostname or Internet address, and port is an integer port number  or
                     service name, bash attempts to open a UDP connection to the corresponding socket.

       A failure to open or create a file causes the redirection to fail.

       Redirections  using  file  descriptors  greater than 9 should be used with care, as they may conflict
       with file descriptors the shell uses internally.

   Redirecting Input
       Redirection of input causes the file whose name results from the expansion of word to be  opened  for
       reading on file descriptor n, or the standard input (file descriptor 0) if n is not specified.

       The general format for redirecting input is:

              [n]<word

   Redirecting Output
       Redirection  of output causes the file whose name results from the expansion of word to be opened for
       writing on file descriptor n, or the standard output (file descriptor 1) if n is not  specified.   If
       the file does not exist it is created; if it does exist it is truncated to zero size.

       The general format for redirecting output is:

              [n]>word

       If  the  redirection operator is >, and the noclobber option to the set builtin has been enabled, the
       redirection will fail if the file whose name results from the expansion of word exists and is a regu-lar regular
       lar  file.   If  the  redirection  operator is >|, or the redirection operator is > and the noclobber
       option to the set builtin command is not enabled, the redirection is attempted even if the file named
       by word exists.

   Appending Redirected Output
       Redirection  of  output in this fashion causes the file whose name results from the expansion of word
       to be opened for appending on file descriptor n, or the standard output (file descriptor 1) if  n  is
       not specified.  If the file does not exist it is created.

       The general format for appending output is:

              [n]>>word


   Redirecting Standard Output and Standard Error
       Bash allows both the standard output (file descriptor 1) and the standard error output (file descrip-tor descriptor
       tor 2) to be redirected to the file whose name is the expansion of word with this construct.

       There are two formats for redirecting standard output and standard error:

              &>word
       and
              >&word

       Of the two forms, the first is preferred.  This is semantically equivalent to

              >word 2>&1

   Here Documents
       This type of redirection instructs the shell to read input from the current source until a line  con-taining containing
       taining only word (with no trailing blanks) is seen.  All of the lines read up to that point are then
       used as the standard input for a command.

       The format of here-documents is:

              <<[-]word
                      here-document
              delimiter

       No parameter expansion, command substitution, arithmetic expansion, or  pathname  expansion  is  per-
       formed  on  word.  If any characters in word are quoted, the delimiter is the result of quote removal
       on word, and the lines in the here-document are not expanded.  If word is unquoted, all lines of  the
       here-document  are  subjected to parameter expansion, command substitution, and arithmetic expansion.
       In the latter case, the character sequence \<newline> is ignored, and \ must be  used  to  quote  the
       characters \, $, and `.

       If the redirection operator is <<-, then all leading tab characters are stripped from input lines and
       the line containing delimiter.  This allows here-documents within shell scripts to be indented  in  a
       natural fashion.

   Here Strings
       A variant of here documents, the format is:

              <<<word

       The word is expanded and supplied to the command on its standard input.

   Duplicating File Descriptors
       The redirection operator

              [n]<&word

       is  used  to  duplicate  input  file  descriptors.   If  word expands to one or more digits, the file
       descriptor denoted by n is made to be a copy of that file descriptor.  If the digits in word  do  not
       specify  a  file descriptor open for input, a redirection error occurs.  If word evaluates to -, file
       descriptor n is closed.  If n is not specified, the standard input (file descriptor 0) is used.

       The operator

              [n]>&word

       is used similarly to duplicate output file descriptors.  If n is not specified, the  standard  output
       (file descriptor 1) is used.  If the digits in word do not specify a file descriptor open for output,
       a redirection error occurs.  As a special case, if n is omitted, and word does not expand to  one  or
       more digits, the standard output and standard error are redirected as described previously.

   Moving File Descriptors
       The redirection operator

              [n]<&digit-

       moves  the file descriptor digit to file descriptor n, or the standard input (file descriptor 0) if n
       is not specified.  digit is closed after being duplicated to n.

       Similarly, the redirection operator

              [n]>&digit-moves [n]>&digitmoves

       moves the file descriptor digit to file descriptor n, or the standard output (file descriptor 1) if n
       is not specified.

   Opening File Descriptors for Reading and Writing
       The redirection operator

              [n]<>word

       causes the file whose name is the expansion of word to be opened for both reading and writing on file
       descriptor n, or on file descriptor 0 if n is not specified.  If the file does not exist, it is  cre-ated. created.
       ated.

ALIASES
       Aliases  allow  a  string  to be substituted for a word when it is used as the first word of a simple
       command.  The shell maintains a list of aliases that may be set and unset with the alias and  unalias
       builtin  commands  (see  SHELL  BUILTIN  COMMANDS  below).  The first word of each simple command, if
       unquoted, is checked to see if it has an alias.  If so, that word is replaced  by  the  text  of  the
       alias.   The  characters  /,  $,  `,  and = and any of the shell metacharacters or quoting characters
       listed above may not appear in an alias name.  The replacement  text  may  contain  any  valid  shell
       input, including shell metacharacters.  The first word of the replacement text is tested for aliases,
       but a word that is identical to an alias being expanded is not expanded a second  time.   This  means
       that  one  may  alias  ls  to  ls  -F,  for instance, and bash does not try to recursively expand the
       replacement text.  If the last character of the alias value is a blank, then the  next  command  word
       following the alias is also checked for alias expansion.

       Aliases are created and listed with the alias command, and removed with the unalias command.

       There  is no mechanism for using arguments in the replacement text.  If arguments are needed, a shell
       function should be used (see FUNCTIONS below).

       Aliases are not expanded when the shell is not interactive, unless the expand_aliases shell option is
       set using shopt (see the description of shopt under SHELL BUILTIN COMMANDS below).

       The  rules concerning the definition and use of aliases are somewhat confusing.  Bash always reads at
       least one complete line of input before executing any of the commands  on  that  line.   Aliases  are
       expanded  when  a command is read, not when it is executed.  Therefore, an alias definition appearing
       on the same line as another command does not take effect until the next line of input is  read.   The
       commands  following the alias definition on that line are not affected by the new alias.  This behav-ior behavior
       ior is also an issue when functions are executed.  Aliases are expanded when a function definition is
       read,  not when the function is executed, because a function definition is itself a compound command.
       As a consequence, aliases defined in a function are not available until after that function  is  exe-cuted. executed.
       cuted.  To be safe, always put alias definitions on a separate line, and do not use alias in compound
       commands.

       For almost every purpose, aliases are superseded by shell functions.

FUNCTIONS
       A shell function, defined as described above under SHELL GRAMMAR, stores a  series  of  commands  for
       later  execution.   When  the  name of a shell function is used as a simple command name, the list of
       commands associated with that function name is executed.  Functions are executed in  the  context  of
       the current shell; no new process is created to interpret them (contrast this with the execution of a
       shell script).  When a function is executed, the arguments to  the  function  become  the  positional
       parameters  during its execution.  The special parameter # is updated to reflect the change.  Special
       parameter 0 is unchanged.  The first element of the FUNCNAME variable is set to the name of the func-tion function
       tion while the function is executing.  All other aspects of the shell execution environment are iden-tical identical
       tical between a function and its caller with the exception that the DEBUG and RETURN traps  (see  the
       description  of  the  trap  builtin  under SHELL BUILTIN COMMANDS below) are not inherited unless the
       function has been given the trace attribute (see the description of the declare builtin below) or the
       -o  functrace shell option has been enabled with the set builtin (in which case all functions inherit
       the DEBUG and RETURN traps).

       Variables local to the function may be declared with the local builtin  command.   Ordinarily,  vari-ables variables
       ables and their values are shared between the function and its caller.

       If the builtin command return is executed in a function, the function completes and execution resumes
       with the next command after the function call.  Any command associated with the RETURN trap  is  exe-cuted executed
       cuted  before  execution resumes.  When a function completes, the values of the positional parameters
       and the special parameter # are restored to the values they had prior to the function's execution.

       Function names and definitions may be listed with the -f option to the  declare  or  typeset  builtin
       commands.   The -F option to declare or typeset will list the function names only (and optionally the
       source file and line number, if the extdebug shell option is enabled).  Functions may be exported  so
       that  subshells automatically have them defined with the -f option to the export builtin.  A function
       definition may be deleted using the -f option to the unset builtin.  Note that  shell  functions  and
       variables  with  the  same  name  may result in multiple identically-named entries in the environment
       passed to the shell's children.  Care should be taken in cases where this may cause a problem.

       Functions may be recursive.  No limit is imposed on the number of recursive calls.

ARITHMETIC EVALUATION
       The shell allows arithmetic expressions to be evaluated, under certain circumstances (see the let and
       declare  builtin commands and Arithmetic Expansion).  Evaluation is done in fixed-width integers with
       no check for overflow, though division by 0 is trapped and flagged as an error.   The  operators  and
       their precedence, associativity, and values are the same as in the C language.  The following list of
       operators is grouped into levels of equal-precedence operators.  The levels are listed  in  order  of
       decreasing precedence.

       id++ id--variable id-variable
              variable post-increment and post-decrement
       ++id --id
              variable pre-increment and pre-decrement
       - +    unary minus and plus
       ! ~    logical and bitwise negation
       **     exponentiation
       * / %  multiplication, division, remainder
       + -    addition, subtraction
       << >>  left and right bitwise shifts
       <= >= < >
              comparison
       == !=  equality and inequality
       &      bitwise AND
       ^      bitwise exclusive OR
       |      bitwise OR
       &&     logical AND
       ||     logical OR
       expr?expr:expr
              conditional operator
       = *= /= %= += -= <<= >>= &= ^= |=
              assignment
       expr1 , expr2
              comma

       Shell  variables  are  allowed as operands; parameter expansion is performed before the expression is
       evaluated.  Within an expression, shell variables may also be referenced by name  without  using  the
       parameter expansion syntax.  A shell variable that is null or unset evaluates to 0 when referenced by
       name without using the parameter expansion syntax.  The value of a variable is evaluated as an arith-metic arithmetic
       metic expression when it is referenced, or when a variable which has been given the integer attribute
       using declare -i is assigned a value.  A null value evaluates to 0.  A shell variable need  not  have
       its integer attribute turned on to be used in an expression.

       Constants with a leading 0 are interpreted as octal numbers.  A leading 0x or 0X denotes hexadecimal.
       Otherwise, numbers take the form [base#]n, where base is a decimal number between 2 and 64 represent-ing representing
       ing  the arithmetic base, and n is a number in that base.  If base# is omitted, then base 10 is used.
       The digits greater than 9 are represented by the lowercase letters, the uppercase letters, @, and  _,
       in  that  order.   If  base  is less than or equal to 36, lowercase and uppercase letters may be used
       interchangeably to represent numbers between 10 and 35.

       Operators are evaluated in order of precedence.  Sub-expressions in parentheses are  evaluated  first
       and may override the precedence rules above.

CONDITIONAL EXPRESSIONS
       Conditional  expressions  are  used by the [[ compound command and the test and [ builtin commands to
       test file attributes and perform string and arithmetic comparisons.  Expressions are formed from  the
       following  unary  or  binary  primaries.  If any file argument to one of the primaries is of the form
       /dev/fd/n, then file descriptor n is checked.  If the file argument to one of the primaries is one of
       /dev/stdin, /dev/stdout, or /dev/stderr, file descriptor 0, 1, or 2, respectively, is checked.

       Unless  otherwise specified, primaries that operate on files follow symbolic links and operate on the
       target of the link, rather than the link itself.

       -a file
              True if file exists.
       -b file
              True if file exists and is a block special file.
       -c file
              True if file exists and is a character special file.
       -d file
              True if file exists and is a directory.
       -e file
              True if file exists.
       -f file
              True if file exists and is a regular file.
       -g file
              True if file exists and is set-group-id.
       -h file
              True if file exists and is a symbolic link.
       -k file
              True if file exists and its ``sticky'' bit is set.
       -p file
              True if file exists and is a named pipe (FIFO).
       -r file
              True if file exists and is readable.
       -s file
              True if file exists and has a size greater than zero.
       -t fd  True if file descriptor fd is open and refers to a terminal.
       -u file
              True if file exists and its set-user-id bit is set.
       -w file
              True if file exists and is writable.
       -x file
              True if file exists and is executable.
       -O file
              True if file exists and is owned by the effective user id.
       -G file
              True if file exists and is owned by the effective group id.
       -L file
              True if file exists and is a symbolic link.
       -S file
              True if file exists and is a socket.
       -N file
              True if file exists and has been modified since it was last read.
       file1 -nt file2
              True if file1 is newer (according to modification date) than file2, or  if  file1  exists  and
              file2 does not.
       file1 -ot file2
              True if file1 is older than file2, or if file2 exists and file1 does not.
       file1 -ef file2
              True if file1 and file2 refer to the same device and inode numbers.
       -o optname
              True if shell option optname is enabled.  See the list of options under the description of the
              -o option to the set builtin below.
       -z string
              True if the length of string is zero.
       string
       -n string
              True if the length of string is non-zero.

       string1 == string2
              True if the strings are equal.  = may be used in place of == for strict POSIX compliance.

       string1 != string2
              True if the strings are not equal.

       string1 < string2
              True if string1 sorts before string2 lexicographically in the current locale.

       string1 > string2
              True if string1 sorts after string2 lexicographically in the current locale.

       arg1 OP arg2
              OP is one of -eq, -ne, -lt, -le, -gt, or -ge.  These arithmetic binary operators  return  true
              if  arg1 is equal to, not equal to, less than, less than or equal to, greater than, or greater
              than or equal to arg2, respectively.  Arg1 and arg2 may be positive or negative integers.

SIMPLE COMMAND EXPANSION
       When a simple command is executed, the shell performs  the  following  expansions,  assignments,  and
       redirections, from left to right.

       1.     The  words  that  the  parser  has marked as variable assignments (those preceding the command
              name) and redirections are saved for later processing.

       2.     The words that are not variable assignments or redirections are expanded.  If any words remain
              after expansion, the first word is taken to be the name of the command and the remaining words
              are the arguments.

       3.     Redirections are performed as described above under REDIRECTION.

       4.     The text after the = in each variable assignment undergoes tilde expansion,  parameter  expan-sion, expansion,
              sion,  command  substitution, arithmetic expansion, and quote removal before being assigned to
              the variable.

       If no command name results, the variable assignments affect the current  shell  environment.   Other-wise, Otherwise,
       wise,  the  variables are added to the environment of the executed command and do not affect the cur-rent current
       rent shell environment.  If any of the assignments attempts to assign a value to a readonly variable,
       an error occurs, and the command exits with a non-zero status.

       If  no command name results, redirections are performed, but do not affect the current shell environ-ment. environment.
       ment.  A redirection error causes the command to exit with a non-zero status.

       If there is a command name left after expansion, execution proceeds as described  below.   Otherwise,
       the command exits.  If one of the expansions contained a command substitution, the exit status of the
       command is the exit status of the last command substitution performed.  If there were no command sub-stitutions, substitutions,
       stitutions, the command exits with a status of zero.

COMMAND EXECUTION
       After  a command has been split into words, if it results in a simple command and an optional list of
       arguments, the following actions are taken.

       If the command name contains no slashes, the shell attempts to locate it.  If there  exists  a  shell
       function  by  that  name, that function is invoked as described above in FUNCTIONS.  If the name does
       not match a function, the shell searches for it in the list of shell builtins.  If a match is  found,
       that builtin is invoked.

       If  the  name  is neither a shell function nor a builtin, and contains no slashes, bash searches each
       element of the PATH for a directory containing an executable file by that name.  Bash uses a hash ta-ble table
       ble to remember the full pathnames of executable files (see hash under SHELL BUILTIN COMMANDS below).
       A full search of the directories in PATH is performed only if the command is not found  in  the  hash
       table.   If  the search is unsuccessful, the shell prints an error message and returns an exit status
       of 127.

       If the search is successful, or if the command name contains one or more slashes, the shell  executes
       the  named program in a separate execution environment.  Argument 0 is set to the name given, and the
       remaining arguments to the command are set to the arguments given, if any.

       If this execution fails because the file is not in executable format, and the file is  not  a  direc-tory, directory,
       tory, it is assumed to be a shell script, a file containing shell commands.  A subshell is spawned to
       execute it.  This subshell reinitializes itself, so that the effect is as if a  new  shell  had  been
       invoked  to  handle  the  script, with the exception that the locations of commands remembered by the
       parent (see hash below under SHELL BUILTIN COMMANDS) are retained by the child.

       If the program is a file beginning with #!, the remainder of the first line specifies an  interpreter
       for  the program.  The shell executes the specified interpreter on operating systems that do not han-dle handle
       dle this executable format themselves.  The arguments to the interpreter consist of a single optional
       argument following the interpreter name on the first line of the program, followed by the name of the
       program, followed by the command arguments, if any.

COMMAND EXECUTION ENVIRONMENT
       The shell has an execution environment, which consists of the following:


             open files inherited by the shell at invocation, as modified by redirections supplied  to  the
              exec builtin

             the current working directory as set by cd, pushd, or popd, or inherited by the shell at invo-cation invocation
              cation

             the file creation mode mask as set by umask or inherited from the shell's parent

             current traps set by trap

             shell parameters that are set by variable assignment or with set or inherited from the shell's
              parent in the environment

             shell  functions defined during execution or inherited from the shell's parent in the environ-ment environment
              ment

             options enabled at invocation (either by default or with command-line arguments) or by set

             options enabled by shopt

             shell aliases defined with alias

             various process IDs, including those of background jobs, the value of $$,  and  the  value  of
              $PPID

       When  a  simple  command other than a builtin or shell function is to be executed, it is invoked in a
       separate execution environment that consists of the following.  Unless otherwise  noted,  the  values
       are inherited from the shell.


             the  shell's open files, plus any modifications and additions specified by redirections to the
              command

             the current working directory

             the file creation mode mask

             shell variables and functions marked for export, along with variables exported  for  the  com-mand, command,
              mand, passed in the environment

             traps caught by the shell are reset to the values inherited from the shell's parent, and traps
              ignored by the shell are ignored

       A command invoked in this separate environment cannot affect the shell's execution environment.

       Command substitution, commands grouped with parentheses, and asynchronous commands are invoked  in  a
       subshell  environment  that  is a duplicate of the shell environment, except that traps caught by the
       shell are reset to the values that the shell inherited from its parent at invocation.   Builtin  com-mands commands
       mands  that  are  invoked as part of a pipeline are also executed in a subshell environment.  Changes
       made to the subshell environment cannot affect the shell's execution environment.

       If a command is followed by a & and job control is not active, the default  standard  input  for  the
       command is the empty file /dev/null.  Otherwise, the invoked command inherits the file descriptors of
       the calling shell as modified by redirections.

ENVIRONMENT
       When a program is invoked it is given an array of strings called the environment.  This is a list  of
       name-value pairs, of the form name=value.

       The  shell  provides  several ways to manipulate the environment.  On invocation, the shell scans its
       own environment and creates a parameter for each name found, automatically marking it for  export  to
       child  processes.   Executed  commands  inherit  the environment.  The export and declare -x commands
       allow parameters and functions to be added to and deleted from the environment.  If the  value  of  a
       parameter  in  the  environment is modified, the new value becomes part of the environment, replacing
       the old.  The environment inherited by any executed command consists of the shell's initial  environ-ment, environment,
       ment,  whose  values  may be modified in the shell, less any pairs removed by the unset command, plus
       any additions via the export and declare -x commands.

       The environment for any simple command or function may be augmented temporarily by prefixing it  with
       parameter assignments, as described above in PARAMETERS.  These assignment statements affect only the
       environment seen by that command.

       If the -k option is set (see the set builtin command  below),  then  all  parameter  assignments  are
       placed in the environment for a command, not just those that precede the command name.

       When bash invokes an external command, the variable _ is set to the full file name of the command and
       passed to that command in its environment.

EXIT STATUS
       For the shell's purposes, a command which exits with a zero exit status has succeeded.  An exit  sta-tus status
       tus  of zero indicates success.  A non-zero exit status indicates failure.  When a command terminates
       on a fatal signal N, bash uses the value of 128+N as the exit status.

       If a command is not found, the child process created to execute it returns a status  of  127.   If  a
       command is found but is not executable, the return status is 126.

       If  a  command  fails because of an error during expansion or redirection, the exit status is greater
       than zero.

       Shell builtin commands return a status of 0 (true) if successful, and non-zero (false)  if  an  error
       occurs while they execute.  All builtins return an exit status of 2 to indicate incorrect usage.

       Bash  itself  returns  the exit status of the last command executed, unless a syntax error occurs, in
       which case it exits with a non-zero value.  See also the exit builtin command below.

SIGNALS
       When bash is interactive, in the absence of any traps, it ignores SIGTERM (so that kill  0  does  not
       kill  an interactive shell), and SIGINT is caught and handled (so that the wait builtin is interrupt-ible). interruptible).
       ible).  In all cases, bash ignores SIGQUIT.  If job control is in effect, bash ignores SIGTTIN, SIGT-TOU, SIGTTOU,
       TOU, and SIGTSTP.

       Non-builtin  commands  run by bash have signal handlers set to the values inherited by the shell from
       its parent.  When job control is not in effect, asynchronous commands ignore SIGINT  and  SIGQUIT  in
       addition  to  these  inherited handlers.  Commands run as a result of command substitution ignore the
       keyboard-generated job control signals SIGTTIN, SIGTTOU, and SIGTSTP.

       The shell exits by default upon receipt of a SIGHUP.  Before exiting, an  interactive  shell  resends
       the  SIGHUP  to  all  jobs,  running  or  stopped.  Stopped jobs are sent SIGCONT to ensure that they
       receive the SIGHUP.  To prevent the shell from sending the signal to a particular job, it  should  be
       removed  from  the jobs table with the disown builtin (see SHELL BUILTIN COMMANDS below) or marked to
       not receive SIGHUP using disown -h.

       If the huponexit shell option has been set with shopt, bash sends a SIGHUP to all jobs when an inter-active interactive
       active login shell exits.

       If bash is waiting for a command to complete and receives a signal for which a trap has been set, the
       trap will not be executed until the command completes.  When bash is waiting for an asynchronous com-mand command
       mand  via  the  wait  builtin, the reception of a signal for which a trap has been set will cause the
       wait builtin to return immediately with an exit status greater than 128, immediately after which  the
       trap is executed.

JOB CONTROL
       Job  control  refers to the ability to selectively stop (suspend) the execution of processes and con-tinue continue
       tinue (resume) their execution at a later point.  A user  typically  employs  this  facility  via  an
       interactive interface supplied jointly by the system's terminal driver and bash.

       The  shell  associates a job with each pipeline.  It keeps a table of currently executing jobs, which
       may be listed with the jobs command.  When bash starts a job asynchronously (in the  background),  it
       prints a line that looks like:

              [1] 25647

       indicating  that this job is job number 1 and that the process ID of the last process in the pipeline
       associated with this job is 25647.  All of the processes in a single pipeline are members of the same
       job.  Bash uses the job abstraction as the basis for job control.

       To facilitate the implementation of the user interface to job control, the operating system maintains
       the notion of a current terminal process group ID.  Members of this process  group  (processes  whose
       process  group  ID is equal to the current terminal process group ID) receive keyboard-generated sig-nals signals
       nals such as SIGINT.  These processes are said to be in the  foreground.   Background  processes  are
       those  whose process group ID differs from the terminal's; such processes are immune to keyboard-gen-erated keyboard-generated
       erated signals.  Only foreground processes are allowed to read from or write to the terminal.   Back-ground Background
       ground processes which attempt to read from (write to) the terminal are sent a SIGTTIN (SIGTTOU) sig-nal signal
       nal by the terminal driver, which, unless caught, suspends the process.

       If the operating system on which bash is running supports job control, bash  contains  facilities  to
       use  it.   Typing  the  suspend character (typically ^Z, Control-Z) while a process is running causes
       that process to be stopped and returns control to bash.  Typing the delayed suspend character  (typi-cally (typically
       cally  ^Y, Control-Y) causes the process to be stopped when it attempts to read input from the termi-nal, terminal,
       nal, and control to be returned to bash.  The user may then manipulate the state of this  job,  using
       the  bg command to continue it in the background, the fg command to continue it in the foreground, or
       the kill command to kill it.  A ^Z takes effect immediately, and has the additional  side  effect  of
       causing pending output and typeahead to be discarded.

       There  are  a  number of ways to refer to a job in the shell.  The character % introduces a job name.
       Job number n may be referred to as %n.  A job may also be referred to using a prefix of the name used
       to  start  it,  or  using a substring that appears in its command line.  For example, %ce refers to a
       stopped ce job.  If a prefix matches more than one job, bash reports an error.  Using  %?ce,  on  the
       other hand, refers to any job containing the string ce in its command line.  If the substring matches
       more than one job, bash reports an error.  The symbols %% and %+ refer to the shell's notion  of  the
       current  job,  which  is  the last job stopped while it was in the foreground or started in the back-ground. background.
       ground.  The previous job may be referenced using %-.  In output pertaining to jobs (e.g., the output
       of  the  jobs command), the current job is always flagged with a +, and the previous job with a -.  A
       single % (with no accompanying job specification) also refers to the current job.

       Simply naming a job can be used to bring it into the foreground: %1  is  a  synonym  for  ``fg  %1'',
       bringing  job  1  from  the background into the foreground.  Similarly, ``%1 &'' resumes job 1 in the
       background, equivalent to ``bg %1''.

       The shell learns immediately whenever a job changes state.  Normally, bash waits until it is about to
       print  a  prompt  before reporting changes in a job's status so as to not interrupt any other output.
       If the -b option to the set builtin command is enabled, bash reports such changes  immediately.   Any
       trap on SIGCHLD is executed for each child that exits.

       If  an  attempt to exit bash is made while jobs are stopped, the shell prints a warning message.  The
       jobs command may then be used to inspect their status.  If a second attempt to exit is  made  without
       an  intervening  command,  the  shell does not print another warning, and the stopped jobs are termi-nated. terminated.
       nated.

PROMPTING
       When executing interactively, bash displays the primary prompt PS1 when it is ready to  read  a  com-mand, command,
       mand, and the secondary prompt PS2 when it needs more input to complete a command.  Bash allows these
       prompt strings to be customized by inserting a number of backslash-escaped  special  characters  that
       are decoded as follows:
              \a     an ASCII bell character (07)
              \d     the date in "Weekday Month Date" format (e.g., "Tue May 26")
              \D{format}
                     the  format is passed to strftime(3) and the result is inserted into the prompt string;
                     an empty format results in a  locale-specific  time  representation.   The  braces  are
                     required
              \e     an ASCII escape character (033)
              \h     the hostname up to the first `.'
              \H     the hostname
              \j     the number of jobs currently managed by the shell
              \l     the basename of the shell's terminal device name
              \n     newline
              \r     carriage return
              \s     the name of the shell, the basename of $0 (the portion following the final slash)
              \t     the current time in 24-hour HH:MM:SS format
              \T     the current time in 12-hour HH:MM:SS format
              \@     the current time in 12-hour am/pm format
              \A     the current time in 24-hour HH:MM format
              \u     the username of the current user
              \v     the version of bash (e.g., 2.00)
              \V     the release of bash, version + patch level (e.g., 2.00.0)
              \w     the current working directory, with $HOME abbreviated with a tilde
              \W     the basename of the current working directory, with $HOME abbreviated with a tilde
              \!     the history number of this command
              \#     the command number of this command
              \$     if the effective UID is 0, a #, otherwise a $
              \nnn   the character corresponding to the octal number nnn
              \\     a backslash
              \[     begin  a  sequence  of non-printing characters, which could be used to embed a terminal
                     control sequence into the prompt
              \]     end a sequence of non-printing characters

       The command number and the history number are usually different: the history number of a  command  is
       its position in the history list, which may include commands restored from the history file (see HIS-TORY HISTORY
       TORY below), while the command number is the position in the sequence of commands executed during the
       current  shell session.  After the string is decoded, it is expanded via parameter expansion, command
       substitution, arithmetic expansion, and quote removal, subject to the value of the  promptvars  shell
       option (see the description of the shopt command under SHELL BUILTIN COMMANDS below).

READLINE
       This  is the library that handles reading input when using an interactive shell, unless the --noedit-ing --noediting
       ing option is given at shell invocation.  By default, the line editing commands are similar to  those
       of  emacs.   A vi-style line editing interface is also available.  To turn off line editing after the
       shell is running, use the +o emacs or +o vi options to the set builtin (see  SHELL  BUILTIN  COMMANDS
       below).

   Readline Notation
       In  this section, the emacs-style notation is used to denote keystrokes.  Control keys are denoted by
       C-key, e.g., C-n means Control-N.  Similarly, meta keys are denoted by M-key, so  M-x  means  Meta-X.
       (On  keyboards  without a meta key, M-x means ESC x, i.e., press the Escape key then the x key.  This
       makes ESC the meta prefix.  The combination M-C-x means ESC-Control-x, or press the Escape  key  then
       hold the Control key while pressing the x key.)

       Readline  commands  may be given numeric arguments, which normally act as a repeat count.  Sometimes,
       however, it is the sign of the argument that is significant.  Passing a negative argument to  a  com-mand command
       mand  that  acts  in the forward direction (e.g., kill-line) causes that command to act in a backward
       direction.  Commands whose behavior with arguments deviates from this are noted below.

       When a command is described as killing text, the text deleted is saved for possible future  retrieval
       (yanking).   The killed text is saved in a kill ring.  Consecutive kills cause the text to be accumu-lated accumulated
       lated into one unit, which can be yanked all at once.  Commands which do not kill text  separate  the
       chunks of text on the kill ring.

   Readline Initialization
       Readline is customized by putting commands in an initialization file (the inputrc file).  The name of
       this file is taken from the value of the INPUTRC variable.  If that variable is unset, the default is
       ~/.inputrc.   When  a  program  which uses the readline library starts up, the initialization file is
       read, and the key bindings and variables are set.  There are only a few basic constructs  allowed  in
       the  readline  initialization file.  Blank lines are ignored.  Lines beginning with a # are comments.
       Lines beginning with a $ indicate conditional constructs.  Other lines denote key bindings and  vari-able variable
       able settings.

       The  default  key-bindings may be changed with an inputrc file.  Other programs that use this library
       may add their own commands and bindings.

       For example, placing

              M-Control-u: universal-argument
       or
              C-Meta-u: universal-argument
       into the inputrc would make M-C-u execute the readline command universal-argument.

       The following symbolic character names are recognized: RUBOUT, DEL, ESC, LFD, NEWLINE,  RET,  RETURN,
       SPC, SPACE, and TAB.

       In  addition to command names, readline allows keys to be bound to a string that is inserted when the
       key is pressed (a macro).

   Readline Key Bindings
       The syntax for controlling key bindings in the inputrc file is simple.  All that is required  is  the
       name  of  the command or the text of a macro and a key sequence to which it should be bound. The name
       may be specified in one of two ways: as a symbolic key name, possibly with  Meta-  or  Control-  pre-fixes, prefixes,
       fixes, or as a key sequence.

       When  using  the  form  keyname:function-name  or  macro, keyname is the name of a key spelled out in
       English.  For example:

              Control-u: universal-argument
              Meta-Rubout: backward-kill-word
              Control-o: "> output"

       In the above example, C-u is bound to the function universal-argument, M-DEL is bound to the function
       backward-kill-word,  and  C-o is bound to run the macro expressed on the right hand side (that is, to
       insert the text ``> output'' into the line).

       In the second form, "keyseq":function-name or macro,  keyseq  differs  from  keyname  above  in  that
       strings  denoting  an  entire  key  sequence  may  be specified by placing the sequence within double
       quotes.  Some GNU Emacs style key escapes can be used, as in the following example, but the  symbolic
       character names are not recognized.

              "\C-u": universal-argument
              "\C-x\C-r": re-read-init-file
              "\e[11~": "Function Key 1"

       In  this  example,  C-u  is  again bound to the function universal-argument.  C-x C-r is bound to the
       function re-read-init-file, and ESC [ 1 1 ~ is bound to insert the text ``Function Key 1''.

       The full set of GNU Emacs style escape sequences is
              \C-    control prefix
              \M-    meta prefix
              \e     an escape character
              \\     backslash
              \"     literal "
              \'     literal '

       In addition to the GNU Emacs style escape sequences, a second set of backslash escapes is available:
              \a     alert (bell)
              \b     backspace
              \d     delete
              \f     form feed
              \n     newline
              \r     carriage return
              \t     horizontal tab
              \v     vertical tab
              \nnn   the eight-bit character whose value is the octal value nnn (one to three digits)
              \xHH   the eight-bit character whose value is the hexadecimal value HH (one or two hex digits)

       When  entering  the text of a macro, single or double quotes must be used to indicate a macro defini-tion. definition.
       tion.  Unquoted text is assumed to be a function name.  In the  macro  body,  the  backslash  escapes
       described  above are expanded.  Backslash will quote any other character in the macro text, including
       " and '.

       Bash allows the current readline key bindings to be displayed or modified with the bind builtin  com-mand. command.
       mand.   The  editing  mode  may  be switched during interactive use by using the -o option to the set
       builtin command (see SHELL BUILTIN COMMANDS below).

   Readline Variables
       Readline has variables that can be used to further customize its behavior.  A variable may be set  in
       the inputrc file with a statement of the form

              set variable-name value

       Except  where  noted,  readline  variables  can  take  the values On or Off (without regard to case).
       Unrecognized variable names are ignored.  When a variable value is read, empty or null  values,  "on"
       (case-insensitive), and "1" are equivalent to On.  All other values are equivalent to Off.  The vari-ables variables
       ables and their default values are:

       bell-style (audible)
              Controls what happens when readline wants to ring the terminal bell.  If set to none, readline
              never  rings  the  bell.  If set to visible, readline uses a visible bell if one is available.
              If set to audible, readline attempts to ring the terminal's bell.
       bind-tty-special-chars (On)
              If set to On, readline attempts to bind the control characters treated specially by  the  ker-nel's kernel's
              nel's terminal driver to their readline equivalents.
       comment-begin (``#'')
              The  string  that is inserted when the readline insert-comment command is executed.  This com-mand command
              mand is bound to M-# in emacs mode and to # in vi command mode.
       completion-ignore-case (Off)
              If set to On, readline performs filename matching and completion in a  case-insensitive  fash-ion. fashion.
              ion.
       completion-query-items (100)
              This determines when the user is queried about viewing the number of possible completions gen-erated generated
              erated by the possible-completions command.  It may be set to any integer value  greater  than
              or equal to zero.  If the number of possible completions is greater than or equal to the value
              of this variable, the user is asked whether or not he wishes to view them; otherwise they  are
              simply listed on the terminal.
       convert-meta (On)
              If  set  to  On,  readline  will  convert  characters  with the eighth bit set to an ASCII key
              sequence by stripping the eighth bit and prefixing  an  escape  character  (in  effect,  using
              escape as the meta prefix).
       disable-completion (Off)
              If  set  to On, readline will inhibit word completion.  Completion characters will be inserted
              into the line as if they had been mapped to self-insert.
       editing-mode (emacs)
              Controls whether readline begins with a set of key bindings similar to  emacs  or  vi.   edit-ing-mode editing-mode
              ing-mode can be set to either emacs or vi.
       enable-keypad (Off)
              When  set  to  On, readline will try to enable the application keypad when it is called.  Some
              systems need this to enable the arrow keys.
       expand-tilde (Off)
              If set to on, tilde expansion is performed when readline attempts word completion.
       history-preserve-point (Off)
              If set to on, the history code attempts to place point at the same location  on  each  history
              line retrieved with previous-history or next-history.
       horizontal-scroll-mode (Off)
              When set to On, makes readline use a single line for display, scrolling the input horizontally
              on a single screen line when it becomes longer than the screen width rather than wrapping to a
              new line.
       input-meta (Off)
              If  set  to  On, readline will enable eight-bit input (that is, it will not strip the high bit
              from the characters it reads), regardless of what the terminal claims  it  can  support.   The
              name meta-flag is a synonym for this variable.
       isearch-terminators (``C-[C-J'')
              The string of characters that should terminate an incremental search without subsequently exe-cuting executing
              cuting the character as a command.  If this variable has not been given a value,  the  charac-ters characters
              ters ESC and C-J will terminate an incremental search.
       keymap (emacs)
              Set  the  current  readline  keymap.   The set of valid keymap names is emacs, emacs-standard,
              emacs-meta, emacs-ctlx, vi, vi-command, and vi-insert.  vi is equivalent to vi-command;  emacs
              is  equivalent  to emacs-standard.  The default value is emacs; the value of editing-mode also
              affects the default keymap.
       mark-directories (On)
              If set to On, completed directory names have a slash appended.
       mark-modified-lines (Off)
              If set to On, history lines that have been modified are displayed with  a  preceding  asterisk
              (*).
       mark-symlinked-directories (Off)
              If  set  to  On, completed names which are symbolic links to directories have a slash appended
              (subject to the value of mark-directories).
       match-hidden-files (On)
              This variable, when set to On, causes readline to match files whose names  begin  with  a  `.'
              (hidden  files) when performing filename completion, unless the leading `.' is supplied by the
              user in the filename to be completed.
       output-meta (Off)
              If set to On, readline will display characters with the eighth bit set directly rather than as
              a meta-prefixed escape sequence.
       page-completions (On)
              If  set  to  On,  readline uses an internal more-like pager to display a screenful of possible
              completions at a time.
       print-completions-horizontally (Off)
              If set to On, readline will display completions with matches sorted horizontally in alphabeti-cal alphabetical
              cal order, rather than down the screen.
       show-all-if-ambiguous (Off)
              This  alters the default behavior of the completion functions.  If set to on, words which have
              more than one possible completion cause the matches to be listed immediately instead of  ring-ing ringing
              ing the bell.
       show-all-if-unmodified (Off)
              This  alters  the  default  behavior  of  the  completion  functions  in  a fashion similar to
              show-all-if-ambiguous.  If set to on, words which have more than one possible completion with-out without
              out  any  possible  partial  completion (the possible completions don't share a common prefix)
              cause the matches to be listed immediately instead of ringing the bell.
       visible-stats (Off)
              If set to On, a character denoting a file's type as reported by stat(2)  is  appended  to  the
              filename when listing possible completions.

   Readline Conditional Constructs
       Readline  implements  a  facility  similar in spirit to the conditional compilation features of the C
       preprocessor which allows key bindings and variable settings to be performed as the result of  tests.
       There are four parser directives used.

       $if    The  $if  construct  allows  bindings to be made based on the editing mode, the terminal being
              used, or the application using readline.  The text of the test extends to the end of the line;
              no characters are required to isolate it.

              mode   The  mode= form of the $if directive is used to test whether readline is in emacs or vi
                     mode.  This may be used in conjunction with the set keymap command,  for  instance,  to
                     set  bindings in the emacs-standard and emacs-ctlx keymaps only if readline is starting
                     out in emacs mode.

              term   The term= form may be used to include terminal-specific key bindings, perhaps  to  bind
                     the  key  sequences output by the terminal's function keys.  The word on the right side
                     of the = is tested against the both full name of the terminal and the  portion  of  the
                     terminal  name  before the first -.  This allows sun to match both sun and sun-cmd, for
                     instance.

              application
                     The application construct is used to include application-specific settings.  Each  pro-gram program
                     gram  using  the readline library sets the application name, and an initialization file
                     can test for a particular value.  This could be used to bind key sequences to functions
                     useful for a specific program.  For instance, the following command adds a key sequence
                     that quotes the current or previous word in Bash:

                     $if Bash
                     # Quote the current or previous word
                     "\C-xq": "\eb\"\ef\""
                     $endif

       $endif This command, as seen in the previous example, terminates an $if command.

       $else  Commands in this branch of the $if directive are executed if the test fails.

       $include
              This directive takes a single filename as an argument and reads  commands  and  bindings  from
              that file.  For example, the following directive would read /etc/inputrc:

              $include  /etc/inputrc

   Searching
       Readline  provides  commands  for searching through the command history (see HISTORY below) for lines
       containing a specified string.  There are two search modes: incremental and non-incremental.

       Incremental searches begin before the user has finished typing the search string.  As each  character
       of  the search string is typed, readline displays the next entry from the history matching the string
       typed so far.  An incremental search requires only as many characters as needed to find  the  desired
       history  entry.   The characters present in the value of the isearch-terminators variable are used to
       terminate an incremental search.  If that variable has not been assigned a value the Escape and  Con-trol-J Control-J
       trol-J  characters  will terminate an incremental search.  Control-G will abort an incremental search
       and restore the original line.  When the search is  terminated,  the  history  entry  containing  the
       search string becomes the current line.

       To find other matching entries in the history list, type Control-S or Control-R as appropriate.  This
       will search backward or forward in the history for the next entry matching the search string typed so
       far.   Any  other key sequence bound to a readline command will terminate the search and execute that
       command.  For instance, a newline will terminate the search and accept the  line,  thereby  executing
       the command from the history list.

       Readline  remembers  the  last  incremental  search  string.  If two Control-Rs are typed without any
       intervening characters defining a new search string, any remembered search string is used.

       Non-incremental searches read the entire search string before starting to search for matching history
       lines.  The search string may be typed by the user or be part of the contents of the current line.

   Readline Command Names
       The  following is a list of the names of the commands and the default key sequences to which they are
       bound.  Command names without an accompanying key sequence are unbound by default.  In the  following
       descriptions, point refers to the current cursor position, and mark refers to a cursor position saved
       by the set-mark command.  The text between the point and mark is referred to as the region.

   Commands for Moving
       beginning-of-line (C-a)
              Move to the start of the current line.
       end-of-line (C-e)
              Move to the end of the line.
       forward-char (C-f)
              Move forward a character.
       backward-char (C-b)
              Move back a character.
       forward-word (M-f)
              Move forward to the end of the next word.  Words are composed of alphanumeric characters (let-ters (letters
              ters and digits).
       backward-word (M-b)
              Move  back  to  the start of the current or previous word.  Words are composed of alphanumeric
              characters (letters and digits).
       clear-screen (C-l)
              Clear the screen leaving the current line at the top of the screen.  With an argument, refresh
              the current line without clearing the screen.
       redraw-current-line
              Refresh the current line.

   Commands for Manipulating the History
       accept-line (Newline, Return)
              Accept  the  line regardless of where the cursor is.  If this line is non-empty, add it to the
              history list according to the state of the HISTCONTROL variable.  If the line  is  a  modified
              history line, then restore the history line to its original state.
       previous-history (C-p)
              Fetch the previous command from the history list, moving back in the list.
       next-history (C-n)
              Fetch the next command from the history list, moving forward in the list.
       beginning-of-history (M-<)
              Move to the first line in the history.
       end-of-history (M->)
              Move to the end of the input history, i.e., the line currently being entered.
       reverse-search-history (C-r)
              Search backward starting at the current line and moving `up' through the history as necessary.
              This is an incremental search.
       forward-search-history (C-s)
              Search forward starting at the current line and moving `down' through the  history  as  neces-sary. necessary.
              sary.  This is an incremental search.
       non-incremental-reverse-search-history (M-p)
              Search  backward  through  the  history  starting  at the current line using a non-incremental
              search for a string supplied by the user.
       non-incremental-forward-search-history (M-n)
              Search forward through the history using a non-incremental search for a string supplied by the
              user.
       history-search-forward
              Search  forward through the history for the string of characters between the start of the cur-rent current
              rent line and the point.  This is a non-incremental search.
       history-search-backward
              Search backward through the history for the string of characters between the start of the cur-rent current
              rent line and the point.  This is a non-incremental search.
       yank-nth-arg (M-C-y)
              Insert  the  first  argument  to the previous command (usually the second word on the previous
              line) at point.  With an argument n, insert the nth word from the previous command (the  words
              in the previous command begin with word 0).  A negative argument inserts the nth word from the
              end of the previous command.  Once the argument n is computed, the argument is extracted as if
              the "!n" history expansion had been specified.
       yank-last-arg (M-., M-_)
              Insert  the  last  argument  to  the  previous  command (the last word of the previous history
              entry).   With  an  argument,  behave  exactly  like  yank-nth-arg.    Successive   calls   to
              yank-last-arg  move back through the history list, inserting the last argument of each line in
              turn.  The history expansion facilities are used to extract the last argument, as if the  "!$"
              history expansion had been specified.
       shell-expand-line (M-C-e)
              Expand  the  line as the shell does.  This performs alias and history expansion as well as all
              of the shell word expansions.  See HISTORY EXPANSION below for a description of history expan-sion. expansion.
              sion.
       history-expand-line (M-^)
              Perform  history expansion on the current line.  See HISTORY EXPANSION below for a description
              of history expansion.
       magic-space
              Perform history expansion on the current line and insert a space.  See HISTORY EXPANSION below
              for a description of history expansion.
       alias-expand-line
              Perform  alias  expansion  on  the current line.  See ALIASES above for a description of alias
              expansion.
       history-and-alias-expand-line
              Perform history and alias expansion on the current line.
       insert-last-argument (M-., M-_)
              A synonym for yank-last-arg.
       operate-and-get-next (C-o)
              Accept the current line for execution and fetch the next line relative  to  the  current  line
              from the history for editing.  Any argument is ignored.
       edit-and-execute-command (C-xC-e)
              Invoke  an editor on the current command line, and execute the result as shell commands.  Bash
              attempts to invoke $FCEDIT, $EDITOR, and emacs as the editor, in that order.

   Commands for Changing Text
       delete-char (C-d)
              Delete the character at point.  If point is at the beginning of the line, there are no charac-ters characters
              ters  in the line, and the last character typed was not bound to delete-char, then return EOF.
       backward-delete-char (Rubout)
              Delete the character behind the cursor.  When given a numeric argument, save the deleted  text
              on the kill ring.
       forward-backward-delete-char
              Delete  the  character under the cursor, unless the cursor is at the end of the line, in which
              case the character behind the cursor is deleted.
       quoted-insert (C-q, C-v)
              Add the next character typed to the line verbatim.  This is how to insert characters like C-q,
              for example.
       tab-insert (C-v TAB)
              Insert a tab character.
       self-insert (a, b, A, 1, !, ...)
              Insert the character typed.
       transpose-chars (C-t)
              Drag  the  character before point forward over the character at point, moving point forward as
              well.  If point is at the end of the line, then this  transposes  the  two  characters  before
              point.  Negative arguments have no effect.
       transpose-words (M-t)
              Drag the word before point past the word after point, moving point over that word as well.  If
              point is at the end of the line, this transposes the last two words on the line.
       upcase-word (M-u)
              Uppercase the current (or following) word.  With a negative argument, uppercase  the  previous
              word, but do not move point.
       downcase-word (M-l)
              Lowercase  the  current (or following) word.  With a negative argument, lowercase the previous
              word, but do not move point.
       capitalize-word (M-c)
              Capitalize the current (or following) word.  With a negative argument, capitalize the previous
              word, but do not move point.
       overwrite-mode
              Toggle  overwrite  mode.   With  an  explicit positive numeric argument, switches to overwrite
              mode.  With an explicit non-positive numeric argument, switches to insert mode.  This  command
              affects  only  emacs mode; vi mode does overwrite differently.  Each call to readline() starts
              in insert mode.  In overwrite mode, characters bound to self-insert replace the text at  point
              rather  than  pushing the text to the right.  Characters bound to backward-delete-char replace
              the character before point with a space.  By default, this command is unbound.

   Killing and Yanking
       kill-line (C-k)
              Kill the text from point to the end of the line.
       backward-kill-line (C-x Rubout)
              Kill backward to the beginning of the line.
       unix-line-discard (C-u)
              Kill backward from point to the beginning of the line.  The killed text is saved on the  kill-ring. killring.
              ring.
       kill-whole-line
              Kill all characters on the current line, no matter where point is.
       kill-word (M-d)
              Kill  from  point  to the end of the current word, or if between words, to the end of the next
              word.  Word boundaries are the same as those used by forward-word.
       backward-kill-word (M-Rubout)
              Kill the word behind point.  Word boundaries are the same as those used by backward-word.
       unix-word-rubout (C-w)
              Kill the word behind point, using white space as a word boundary.  The killed text is saved on
              the kill-ring.
       unix-filename-rubout
              Kill  the word behind point, using white space and the slash character as the word boundaries.
              The killed text is saved on the kill-ring.
       delete-horizontal-space (M-\)
              Delete all spaces and tabs around point.
       kill-region
              Kill the text in the current region.
       copy-region-as-kill
              Copy the text in the region to the kill buffer.
       copy-backward-word
              Copy the word before point to the kill buffer.  The word boundaries  are  the  same  as  back-ward-word. backward-word.
              ward-word.
       copy-forward-word
              Copy  the  word  following point to the kill buffer.  The word boundaries are the same as for-ward-word. forward-word.
              ward-word.
       yank (C-y)
              Yank the top of the kill ring into the buffer at point.
       yank-pop (M-y)
              Rotate the kill ring, and yank the new top.  Only works following yank or yank-pop.

   Numeric Arguments
       digit-argument (M-0, M-1, ..., M--)
              Add this digit to the argument already accumulating, or start a new argument.   M--  starts  a
              negative argument.
       universal-argument
              This  is  another way to specify an argument.  If this command is followed by one or more dig-its, digits,
              its, optionally with a leading minus sign, those digits define the argument.  If  the  command
              is  followed  by  digits, executing universal-argument again ends the numeric argument, but is
              otherwise ignored.  As a special case, if this command is immediately followed by a  character
              that  is  neither a digit or minus sign, the argument count for the next command is multiplied
              by four.  The argument count is initially one, so executing this function the first time makes
              the argument count four, a second time makes the argument count sixteen, and so on.

   Completing
       complete (TAB)
              Attempt to perform completion on the text before point.  Bash attempts completion treating the
              text as a variable (if the text begins with $), username (if the text begins with ~), hostname
              (if the text begins with @), or command (including aliases and functions) in turn.  If none of
              these produces a match, filename completion is attempted.
       possible-completions (M-?)
              List the possible completions of the text before point.
       insert-completions (M-*)
              Insert all completions of the text before point that  would  have  been  generated  by  possi-ble-completions. possible-completions.
              ble-completions.
       menu-complete
              Similar  to  complete, but replaces the word to be completed with a single match from the list
              of possible completions.  Repeated execution of menu-complete steps through the list of possi-ble possible
              ble  completions,  inserting  each  match in turn.  At the end of the list of completions, the
              bell is rung (subject to the setting of bell-style) and the original  text  is  restored.   An
              argument  of  n  moves  n positions forward in the list of matches; a negative argument may be
              used to move backward through the list.  This command is intended to be bound to TAB,  but  is
              unbound by default.
       delete-char-or-list
              Deletes  the  character  under  the  cursor  if  not at the beginning or end of the line (like
              delete-char).  If at the end of the line, behaves identically to  possible-completions.   This
              command is unbound by default.
       complete-filename (M-/)
              Attempt filename completion on the text before point.
       possible-filename-completions (C-x /)
              List the possible completions of the text before point, treating it as a filename.
       complete-username (M-~)
              Attempt completion on the text before point, treating it as a username.
       possible-username-completions (C-x ~)
              List the possible completions of the text before point, treating it as a username.
       complete-variable (M-$)
              Attempt completion on the text before point, treating it as a shell variable.
       possible-variable-completions (C-x $)
              List the possible completions of the text before point, treating it as a shell variable.
       complete-hostname (M-@)
              Attempt completion on the text before point, treating it as a hostname.
       possible-hostname-completions (C-x @)
              List the possible completions of the text before point, treating it as a hostname.
       complete-command (M-!)
              Attempt  completion  on the text before point, treating it as a command name.  Command comple-tion completion
              tion attempts to match the text  against  aliases,  reserved  words,  shell  functions,  shell
              builtins, and finally executable filenames, in that order.
       possible-command-completions (C-x !)
              List the possible completions of the text before point, treating it as a command name.
       dynamic-complete-history (M-TAB)
              Attempt completion on the text before point, comparing the text against lines from the history
              list for possible completion matches.
       complete-into-braces (M-{)
              Perform filename completion and insert the list of possible completions enclosed within braces
              so the list is available to the shell (see Brace Expansion above).

   Keyboard Macros
       start-kbd-macro (C-x ()
              Begin saving the characters typed into the current keyboard macro.
       end-kbd-macro (C-x ))
              Stop saving the characters typed into the current keyboard macro and store the definition.
       call-last-kbd-macro (C-x e)
              Re-execute the last keyboard macro defined, by making the characters in the macro appear as if
              typed at the keyboard.

   Miscellaneous
       re-read-init-file (C-x C-r)
              Read in the contents of the inputrc file, and incorporate any bindings or variable assignments
              found there.
       abort (C-g)
              Abort  the  current  editing  command  and ring the terminal's bell (subject to the setting of
              bell-style).
       do-uppercase-version (M-a, M-b, M-x, ...)
              If the metafied character x is lowercase, run the command that is bound to  the  corresponding
              uppercase character.
       prefix-meta (ESC)
              Metafy the next character typed.  ESC f is equivalent to Meta-f.
       undo (C-_, C-x C-u)
              Incremental undo, separately remembered for each line.
       revert-line (M-r)
              Undo  all  changes made to this line.  This is like executing the undo command enough times to
              return the line to its initial state.
       tilde-expand (M-&)
              Perform tilde expansion on the current word.
       set-mark (C-@, M-<space>)
              Set the mark to the point.  If a numeric argument is supplied, the mark is set to  that  posi-tion. position.
              tion.
       exchange-point-and-mark (C-x C-x)
              Swap  the  point with the mark.  The current cursor position is set to the saved position, and
              the old cursor position is saved as the mark.
       character-search (C-])
              A character is read and point is moved to the next occurrence of that character.   A  negative
              count searches for previous occurrences.
       character-search-backward (M-C-])
              A  character is read and point is moved to the previous occurrence of that character.  A nega-tive negative
              tive count searches for subsequent occurrences.
       insert-comment (M-#)
              Without a numeric argument, the value of the readline comment-begin variable  is  inserted  at
              the  beginning of the current line.  If a numeric argument is supplied, this command acts as a
              toggle:  if the characters at the beginning of the  line  do  not  match  the  value  of  com-ment-begin, comment-begin,
              ment-begin,  the value is inserted, otherwise the characters in comment-begin are deleted from
              the beginning of the line.  In either case, the line is accepted as  if  a  newline  had  been
              typed.   The  default  value  of  comment-begin causes this command to make the current line a
              shell comment.  If a numeric argument causes the comment character to  be  removed,  the  line
              will be executed by the shell.
       glob-complete-word (M-g)
              The word before point is treated as a pattern for pathname expansion, with an asterisk implic-itly implicitly
              itly appended.  This pattern is used to generate a list of matching file  names  for  possible
              completions.
       glob-expand-word (C-x *)
              The word before point is treated as a pattern for pathname expansion, and the list of matching
              file names is inserted, replacing the word.  If a numeric argument is supplied, an asterisk is
              appended before pathname expansion.
       glob-list-expansions (C-x g)
              The  list  of  expansions that would have been generated by glob-expand-word is displayed, and
              the line is redrawn.  If a numeric argument is supplied, an asterisk is appended before  path-name pathname
              name expansion.
       dump-functions
              Print all of the functions and their key bindings to the readline output stream.  If a numeric
              argument is supplied, the output is formatted in such a way that it can be  made  part  of  an
              inputrc file.
       dump-variables
              Print  all  of the settable readline variables and their values to the readline output stream.
              If a numeric argument is supplied, the output is formatted in such a way that it can  be  made
              part of an inputrc file.
       dump-macros
              Print  all  of  the  readline key sequences bound to macros and the strings they output.  If a
              numeric argument is supplied, the output is formatted in such a way that it can be  made  part
              of an inputrc file.
       display-shell-version (C-x C-v)
              Display version information about the current instance of bash.

   Programmable Completion
       When  word  completion is attempted for an argument to a command for which a completion specification
       (a compspec) has been defined using the complete builtin (see SHELL BUILTIN COMMANDS below), the pro-grammable programmable
       grammable completion facilities are invoked.

       First, the command name is identified.  If a compspec has been defined for that command, the compspec
       is used to generate the list of possible completions for the word.  If the command  word  is  a  full
       pathname,  a  compspec  for the full pathname is searched for first.  If no compspec is found for the
       full pathname, an attempt is made to find a compspec for the portion following the final slash.

       Once a compspec has been found, it is used to generate the list of matching words.  If a compspec  is
       not found, the default bash completion as described above under Completing is performed.

       First,  the  actions specified by the compspec are used.  Only matches which are prefixed by the word
       being completed are returned.  When the -f or -d option is used for filename or directory  name  com-pletion, completion,
       pletion, the shell variable FIGNORE is used to filter the matches.

       Any  completions  specified by a filename expansion pattern to the -G option are generated next.  The
       words generated by the pattern need not match the word being completed.  The GLOBIGNORE  shell  vari-able variable
       able is not used to filter the matches, but the FIGNORE variable is used.

       Next, the string specified as the argument to the -W option is considered.  The string is first split
       using the characters in the IFS special variable as delimiters.  Shell quoting is honored.  Each word
       is  then  expanded  using brace expansion, tilde expansion, parameter and variable expansion, command
       substitution, and arithmetic expansion, as described above under EXPANSION.  The  results  are  split
       using  the  rules  described  above  under  Word Splitting.  The results of the expansion are prefix-matched prefixmatched
       matched against the word being completed, and the matching words become the possible completions.

       After these matches have been generated, any shell function or command specified with the -F  and  -C
       options  is invoked.  When the command or function is invoked, the COMP_LINE and COMP_POINT variables
       are assigned values as described above under Shell Variables.  If a shell function is being  invoked,
       the  COMP_WORDS  and COMP_CWORD variables are also set.  When the function or command is invoked, the
       first argument is the name of the command whose arguments are being completed, the second argument is
       the  word  being  completed, and the third argument is the word preceding the word being completed on
       the current command line.  No filtering of the generated completions against the word being completed
       is performed; the function or command has complete freedom in generating the matches.

       Any  function  specified with -F is invoked first.  The function may use any of the shell facilities,
       including the compgen builtin described below, to generate the matches.  It  must  put  the  possible
       completions in the COMPREPLY array variable.

       Next,  any  command  specified  with the -C option is invoked in an environment equivalent to command
       substitution.  It should print a list of completions, one per line, to the  standard  output.   Back-slash Backslash
       slash may be used to escape a newline, if necessary.

       After  all  of  the  possible  completions  are generated, any filter specified with the -X option is
       applied to the list.  The filter is a pattern as used for pathname expansion; a & in the  pattern  is
       replaced with the text of the word being completed.  A literal & may be escaped with a backslash; the
       backslash is removed before attempting a match.  Any completion that  matches  the  pattern  will  be
       removed from the list.  A leading ! negates the pattern; in this case any completion not matching the
       pattern will be removed.

       Finally, any prefix and suffix specified with the -P and -S options are added to each member  of  the
       completion  list,  and the result is returned to the readline completion code as the list of possible
       completions.

       If the previously-applied actions do not generate any matches, and the -o dirnames  option  was  sup-plied supplied
       plied to complete when the compspec was defined, directory name completion is attempted.

       If the -o plusdirs option was supplied to complete when the compspec was defined, directory name com-pletion completion
       pletion is attempted and any matches are added to the results of the other actions.

       By default, if a compspec is found, whatever it generates is returned to the completion code  as  the
       full  set  of possible completions.  The default bash completions are not attempted, and the readline
       default of filename completion is disabled.  If the -o bashdefault option was  supplied  to  complete
       when  the  compspec was defined, the bash default completions are attempted if the compspec generates
       no matches.  If the -o default option was supplied to complete when the compspec was  defined,  read-line's readline's
       line's default completion will be performed if the compspec (and, if attempted, the default bash com-pletions) completions)
       pletions) generate no matches.

       When a compspec indicates that directory name completion  is  desired,  the  programmable  completion
       functions  force  readline  to append a slash to completed names which are symbolic links to directo-ries, directories,
       ries, subject to the value of the mark-directories readline variable, regardless of  the  setting  of
       the mark-symlinked-directories readline variable.

HISTORY
       When  the  -o  history option to the set builtin is enabled, the shell provides access to the command
       history, the list of commands previously typed.  The value of the HISTSIZE variable is  used  as  the
       number  of  commands to save in a history list.  The text of the last HISTSIZE commands (default 500)
       is saved.  The shell stores each command in the history list prior to parameter and  variable  expan-sion expansion
       sion  (see  EXPANSION  above)  but after history expansion is performed, subject to the values of the
       shell variables HISTIGNORE and HISTCONTROL.

       On startup, the history is initialized  from  the  file  named  by  the  variable  HISTFILE  (default
       ~/.bash_history).   The file named by the value of HISTFILE is truncated, if necessary, to contain no
       more than the number of lines specified by the value of  HISTFILESIZE.   When  an  interactive  shell
       exits,  the  last  $HISTSIZE  lines are copied from the history list to $HISTFILE.  If the histappend
       shell option is enabled (see the description of shopt under SHELL BUILTIN COMMANDS below), the  lines
       are  appended  to the history file, otherwise the history file is overwritten.  If HISTFILE is unset,
       or if the history file is unwritable, the history is not saved.  After saving the history,  the  his-tory history
       tory  file  is  truncated to contain no more than HISTFILESIZE lines.  If HISTFILESIZE is not set, no
       truncation is performed.

       The builtin command fc (see SHELL BUILTIN COMMANDS below) may be used to list or edit and  re-execute
       a portion of the history list.  The history builtin may be used to display or modify the history list
       and manipulate the history file.  When using command-line editing, search commands are  available  in
       each editing mode that provide access to the history list.

       The  shell  allows  control  over  which commands are saved on the history list.  The HISTCONTROL and
       HISTIGNORE variables may be set to cause the shell to save only a subset  of  the  commands  entered.
       The  cmdhist  shell option, if enabled, causes the shell to attempt to save each line of a multi-line
       command in the same history entry, adding semicolons where necessary to preserve  syntactic  correct-ness. correctness.
       ness.   The  lithist shell option causes the shell to save the command with embedded newlines instead
       of semicolons.  See the description of the shopt builtin  below  under  SHELL  BUILTIN  COMMANDS  for
       information on setting and unsetting shell options.

HISTORY EXPANSION
       The shell supports a history expansion feature that is similar to the history expansion in csh.  This
       section describes what syntax features are available.  This feature is enabled by default for  inter-active interactive
       active  shells, and can be disabled using the +H option to the set builtin command (see SHELL BUILTIN
       COMMANDS below).  Non-interactive shells do not perform history expansion by default.

       History expansions introduce words from the history list into the input stream,  making  it  easy  to
       repeat  commands,  insert  the  arguments  to  a previous command into the current input line, or fix
       errors in previous commands quickly.

       History expansion is performed immediately after a complete line is read, before the shell breaks  it
       into words.  It takes place in two parts.  The first is to determine which line from the history list
       to use during substitution.  The second is to select portions of that line  for  inclusion  into  the
       current one.  The line selected from the history is the event, and the portions of that line that are
       acted upon are words.  Various modifiers are available to manipulate the selected words.  The line is
       broken  into words in the same fashion as when reading input, so that several metacharacter-separated
       words surrounded by quotes are considered one word.  History expansions are introduced by the appear-ance appearance
       ance of the history expansion character, which is ! by default.  Only backslash (\) and single quotes
       can quote the history expansion character.

       Several characters inhibit history expansion if found immediately  following  the  history  expansion
       character, even if it is unquoted: space, tab, newline, carriage return, and =.  If the extglob shell
       option is enabled, ( will also inhibit expansion.

       Several shell options settable with the shopt builtin may be used to tailor the behavior  of  history
       expansion.  If the histverify shell option is enabled (see the description of the shopt builtin), and
       readline is being used, history substitutions  are  not  immediately  passed  to  the  shell  parser.
       Instead, the expanded line is reloaded into the readline editing buffer for further modification.  If
       readline is being used, and the histreedit shell option is enabled,  a  failed  history  substitution
       will  be  reloaded  into  the  readline  editing buffer for correction.  The -p option to the history
       builtin command may be used to see what a history expansion will do before using it.  The  -s  option
       to  the  history  builtin may be used to add commands to the end of the history list without actually
       executing them, so that they are available for subsequent recall.

       The shell allows control of the various characters used by the history expansion mechanism  (see  the
       description of histchars above under Shell Variables).

   Event Designators
       An event designator is a reference to a command line entry in the history list.

       !      Start  a history substitution, except when followed by a blank, newline, carriage return, = or
              ( (when the extglob shell option is enabled using the shopt builtin).
       !n     Refer to command line n.
       !-n    Refer to the current command line minus n.
       !!     Refer to the previous command.  This is a synonym for `!-1'.
       !string
              Refer to the most recent command starting with string.
       !?string[?]
              Refer to the most recent command containing string.  The trailing ? may be omitted  if  string
              is followed immediately by a newline.
       ^string1^string2^
              Quick  substitution.   Repeat the last command, replacing string1 with string2.  Equivalent to
              ``!!:s/string1/string2/'' (see Modifiers below).
       !#     The entire command line typed so far.

   Word Designators
       Word designators are used to select desired words from the event.  A : separates the event specifica-tion specification
       tion from the word designator.  It may be omitted if the word designator begins with a ^, $, *, -, or
       %.  Words are numbered from the beginning of the line, with the first word being denoted by 0 (zero).
       Words are inserted into the current line separated by single spaces.

       0 (zero)
              The zeroth word.  For the shell, this is the command word.
       n      The nth word.
       ^      The first argument.  That is, word 1.
       $      The last argument.
       %      The word matched by the most recent `?string?' search.
       x-y    A range of words; `-y' abbreviates `0-y'.
       *      All of the words but the zeroth.  This is a synonym for `1-$'.  It is not an error to use * if
              there is just one word in the event; the empty string is returned in that case.
       x*     Abbreviates x-$.
       x-     Abbreviates x-$ like x*, but omits the last word.

       If a word designator is supplied without an event specification, the previous command is used as  the
       event.

   Modifiers
       After the optional word designator, there may appear a sequence of one or more of the following modi-fiers, modifiers,
       fiers, each preceded by a `:'.

       h      Remove a trailing file name component, leaving only the head.
       t      Remove all leading file name components, leaving the tail.
       r      Remove a trailing suffix of the form .xxx, leaving the basename.
       e      Remove all but the trailing suffix.
       p      Print the new command but do not execute it.
       q      Quote the substituted words, escaping further substitutions.
       x      Quote the substituted words as with q, but break into words at blanks and newlines.
       s/old/new/
              Substitute new for the first occurrence of old in the event line.  Any delimiter can  be  used
              in place of /.  The final delimiter is optional if it is the last character of the event line.
              The delimiter may be quoted in old and new with a single backslash.  If & appears in  new,  it
              is  replaced  by  old.  A single backslash will quote the &.  If old is null, it is set to the
              last old substituted, or, if no previous history substitutions took place, the last string  in
              a !?string[?]  search.
       &      Repeat the previous substitution.
       g      Cause changes to be applied over the entire event line.  This is used in conjunction with `:s'
              (e.g., `:gs/old/new/') or `:&'.  If used with `:s', any delimiter can be used in place  of  /,
              and  the  final delimiter is optional if it is the last character of the event line.  An a may
              be used as a synonym for g.
       G      Apply the following `s' modifier once to each word in the event line.

SHELL BUILTIN COMMANDS
       Unless otherwise noted, each builtin command documented in this section as accepting options preceded
       by  -  accepts  --  to  signify  the  end  of the options.  For example, the :, true, false, and test
       builtins do not accept options.
       : [arguments]
              No effect; the command does nothing beyond expanding arguments and  performing  any  specified
              redirections.  A zero exit code is returned.

        .  filename [arguments]
       source filename [arguments]
              Read  and  execute commands from filename in the current shell environment and return the exit
              status of the last command executed from filename.  If filename does not contain a slash, file
              names  in  PATH  are used to find the directory containing filename.  The file searched for in
              PATH need not be executable.  When bash is  not  in  posix  mode,  the  current  directory  is
              searched  if  no file is found in PATH.  If the sourcepath option to the shopt builtin command
              is turned off, the PATH is not searched.  If any arguments are supplied, they become the posi-tional positional
              tional  parameters  when  filename  is  executed.   Otherwise  the  positional  parameters are
              unchanged.  The return status is the status of the last command exited within the script (0 if
              no commands are executed), and false if filename is not found or cannot be read.

       alias [-p] [name[=value] ...]
              Alias  with  no  arguments  or with the -p option prints the list of aliases in the form alias
              name=value on standard output.  When arguments are supplied, an alias is defined for each name
              whose value is given.  A trailing space in  value causes the next word to be checked for alias
              substitution when the alias is expanded.  For each name in the  argument  list  for  which  no
              value  is  supplied,  the name and value of the alias is printed.  Alias returns true unless a
              name is given for which no alias has been defined.

       bg [jobspec ...]
              Resume each suspended job jobspec in the background, as if it had been  started  with  &.   If
              jobspec  is  not present, the shell's notion of the current job is used.  bg jobspec returns 0
              unless run when job control is disabled or, when run with job control enabled,  any  specified
              jobspec was not found or was started without job control.

       bind [-m keymap] [-lpsvPSV]
       bind [-m keymap] [-q function] [-u function] [-r keyseq]
       bind [-m keymap] -f filename
       bind [-m keymap] -x keyseq:shell-command
       bind [-m keymap] keyseq:function-name
       bind readline-command
              Display current readline key and function bindings, bind a key sequence to a readline function
              or macro, or set a readline variable.  Each non-option argument  is  a  command  as  it  would
              appear  in  .inputrc, but each binding or command must be passed as a separate argument; e.g.,
              '"\C-x\C-r": re-read-init-file'.  Options, if supplied, have the following meanings:
              -m keymap
                     Use keymap as the keymap to be affected by the subsequent bindings.  Acceptable  keymap
                     names  are  emacs, emacs-standard, emacs-meta, emacs-ctlx, vi, vi-move, vi-command, and
                     vi-insert.  vi is equivalent to vi-command; emacs is equivalent to emacs-standard.
              -l     List the names of all readline functions.
              -p     Display readline function names and bindings in such a way that they can be re-read.
              -P     List current readline function names and bindings.
              -v     Display readline variable names and values in such a way that they can be re-read.
              -V     List current readline variable names and values.
              -s     Display readline key sequences bound to macros and the strings they output  in  such  a
                     way that they can be re-read.
              -S     Display readline key sequences bound to macros and the strings they output.
              -f filename
                     Read key bindings from filename.
              -q function
                     Query about which keys invoke the named function.
              -u function
                     Unbind all keys bound to the named function.
              -r keyseq
                     Remove any current binding for keyseq.
              -x keyseq:shell-command
                     Cause shell-command to be executed whenever keyseq is entered.

              The return value is 0 unless an unrecognized option is given or an error occurred.

       break [n]
              Exit  from  within a for, while, until, or select loop.  If n is specified, break n levels.  n
              must be >= 1.  If n is greater than the number of enclosing loops,  all  enclosing  loops  are
              exited.   The  return  value  is 0 unless the shell is not executing a loop when break is exe-cuted. executed.
              cuted.

       builtin shell-builtin [arguments]
              Execute the specified shell builtin, passing it arguments, and return its exit  status.   This
              is  useful  when  defining a function whose name is the same as a shell builtin, retaining the
              functionality of the builtin within the function.  The cd builtin is commonly  redefined  this
              way.  The return status is false if shell-builtin is not a shell builtin command.

       cd [-L|-P] [dir]
              Change  the  current  directory  to  dir.  The variable HOME is the default dir.  The variable
              CDPATH defines the search path for the directory containing dir.  Alternative directory  names
              in  CDPATH  are  separated by a colon (:).  A null directory name in CDPATH is the same as the
              current directory, i.e., ``.''.  If dir begins with a slash (/), then CDPATH is not used.  The
              -P  option  says  to  use the physical directory structure instead of following symbolic links
              (see also the -P option to the set builtin command); the -L option forces symbolic links to be
              followed.   An  argument  of  -  is equivalent to $OLDPWD.  If a non-empty directory name from
              CDPATH is used, or if - is the first argument, and the directory  change  is  successful,  the
              absolute  pathname of the new working directory is written to the standard output.  The return
              value is true if the directory was successfully changed; false otherwise.

       caller [expr]
              Returns the context of any active subroutine call (a shell function or a script executed  with
              the  .  or source builtins.  Without expr, caller displays the line number and source filename
              of the current subroutine call.  If a non-negative integer is supplied as  expr,  caller  dis-plays displays
              plays  the line number, subroutine name, and source file corresponding to that position in the
              current execution call stack.  This extra information may be used, for  example,  to  print  a
              stack  trace.   The  current  frame is frame 0.  The return value is 0 unless the shell is not
              executing a subroutine call or expr does not correspond to a valid position in the call stack.

       command [-pVv] command [arg ...]
              Run  command  with args suppressing the normal shell function lookup. Only builtin commands or
              commands found in the PATH are executed.  If the -p option is given, the search for command is
              performed using a default value for PATH that is guaranteed to find all of the standard utili-ties. utilities.
              ties.  If either the -V or -v option is supplied, a description of command is printed.  The -v
              option  causes  a single word indicating the command or file name used to invoke command to be
              displayed; the -V option produces a more verbose description.  If the -V or -v option is  sup-plied, supplied,
              plied, the exit status is 0 if command was found, and 1 if not.  If neither option is supplied
              and an error occurred or command cannot be found, the exit status is 127.  Otherwise, the exit
              status of the command builtin is the exit status of command.

       compgen [option] [word]
              Generate  possible  completion  matches  for  word  according to the options, which may be any
              option accepted by the complete builtin with the exception of -p and -r, and write the matches
              to  the  standard output.  When using the -F or -C options, the various shell variables set by
              the programmable completion facilities, while available, will not have useful values.

              The matches will be generated in the same way as if the programmable completion code had  gen-erated generated
              erated  them  directly from a completion specification with the same flags.  If word is speci-fied, specified,
              fied, only those completions matching word will be displayed.

              The return value is true unless an invalid option is supplied, or no matches were generated.

       complete [-abcdefgjksuv] [-o comp-option] [-A action] [-G globpat] [-W wordlist] [-P prefix] [-S suf-fix] suffix]
       fix]
              [-X filterpat] [-F function] [-C command] name [name ...]
       complete -pr [name ...]
              Specify how arguments to each name should be completed.  If the -p option is supplied,  or  if
              no  options  are supplied, existing completion specifications are printed in a way that allows
              them to be reused as input.  The -r option removes a completion specification for  each  name,
              or, if no names are supplied, all completion specifications.

              The  process  of applying these completion specifications when word completion is attempted is
              described above under Programmable Completion.

              Other options, if specified, have the following meanings.  The arguments to the -G, -W, and -X
              options  (and,  if  necessary,  the  -P  and -S options) should be quoted to protect them from
              expansion before the complete builtin is invoked.
              -o comp-option
                      The comp-option controls several aspects of the compspec's behavior beyond the  simple
                      generation of completions.  comp-option may be one of:
                      bashdefault
                              Perform  the rest of the default bash completions if the compspec generates no
                              matches.
                      default Use readline's default  filename  completion  if  the  compspec  generates  no
                              matches.
                      dirnames
                              Perform directory name completion if the compspec generates no matches.
                      filenames
                              Tell  readline  that  the  compspec generates filenames, so it can perform any
                              filename-specific processing (like adding a slash to directory names  or  sup-pressing suppressing
                              pressing trailing spaces).  Intended to be used with shell functions.
                      nospace Tell  readline  not  to append a space (the default) to words completed at the
                              end of the line.
                      plusdirs
                              After any matches defined by the compspec are generated, directory  name  com-pletion completion
                              pletion  is  attempted  and  any matches are added to the results of the other
                              actions.
              -A action
                      The action may be one of the following to generate a list of possible completions:
                      alias   Alias names.  May also be specified as -a.
                      arrayvar
                              Array variable names.
                      binding Readline key binding names.
                      builtin Names of shell builtin commands.  May also be specified as -b.
                      command Command names.  May also be specified as -c.
                      directory
                              Directory names.  May also be specified as -d.
                      disabled
                              Names of disabled shell builtins.
                      enabled Names of enabled shell builtins.
                      export  Names of exported shell variables.  May also be specified as -e.
                      file    File names.  May also be specified as -f.
                      function
                              Names of shell functions.
                      group   Group names.  May also be specified as -g.
                      helptopic
                              Help topics as accepted by the help builtin.
                      hostname
                              Hostnames, as taken from the file specified by the HOSTFILE shell variable.
                      job     Job names, if job control is active.  May also be specified as -j.
                      keyword Shell reserved words.  May also be specified as -k.
                      running Names of running jobs, if job control is active.
                      service Service names.  May also be specified as -s.
                      setopt  Valid arguments for the -o option to the set builtin.
                      shopt   Shell option names as accepted by the shopt builtin.
                      signal  Signal names.
                      stopped Names of stopped jobs, if job control is active.
                      user    User names.  May also be specified as -u.
                      variable
                              Names of all shell variables.  May also be specified as -v.
              -G globpat
                      The filename expansion pattern globpat is expanded to generate  the  possible  comple-tions. completions.
                      tions.
              -W wordlist
                      The  wordlist is split using the characters in the IFS special variable as delimiters,
                      and each resultant word is expanded.  The possible completions are the members of  the
                      resultant list which match the word being completed.
              -C command
                      command  is executed in a subshell environment, and its output is used as the possible
                      completions.
              -F function
                      The shell function function is executed in the current  shell  environment.   When  it
                      finishes, the possible completions are retrieved from the value of the COMPREPLY array
                      variable.
              -X filterpat
                      filterpat is a pattern as used for filename expansion.  It is applied to the  list  of
                      possible  completions  generated by the preceding options and arguments, and each com-pletion completion
                      pletion matching filterpat is removed from the list.  A leading ! in filterpat negates
                      the pattern; in this case, any completion not matching filterpat is removed.
              -P prefix
                      prefix  is  added at the beginning of each possible completion after all other options
                      have been applied.
              -S suffix
                      suffix is appended to each possible completion  after  all  other  options  have  been
                      applied.

              The  return  value is true unless an invalid option is supplied, an option other than -p or -r
              is supplied without a name argument, an attempt is made to remove a  completion  specification
              for  a name for which no specification exists, or an error occurs adding a completion specifi-cation. specification.
              cation.

       continue [n]
              Resume the next iteration of the enclosing for, while, until, or select loop.  If n is  speci-fied, specified,
              fied,  resume  at the nth enclosing loop.  n must be >= 1.  If n is greater than the number of
              enclosing loops, the last enclosing loop (the ``top-level''  loop)  is  resumed.   The  return
              value is 0 unless the shell is not executing a loop when continue is executed.

       declare [-afFirtx] [-p] [name[=value] ...]
       typeset [-afFirtx] [-p] [name[=value] ...]
              Declare  variables and/or give them attributes.  If no names are given then display the values
              of variables.  The -p option will display the attributes and values of each name.  When -p  is
              used,  additional options are ignored.  The -F option inhibits the display of function defini-tions; definitions;
              tions; only the function name and attributes are printed.  If the  extdebug  shell  option  is
              enabled  using  shopt,  the source file name and line number where the function is defined are
              displayed as well.  The -F option implies -f.  The following options can be used  to  restrict
              output to variables with the specified attribute or to give variables attributes:
              -a     Each name is an array variable (see Arrays above).
              -f     Use function names only.
              -i     The variable is treated as an integer; arithmetic evaluation (see ARITHMETIC EVALUATION
                     ) is performed when the variable is assigned a value.
              -r     Make names readonly.  These names cannot then be assigned values by subsequent  assign-ment assignment
                     ment statements or unset.
              -t     Give  each  name  the  trace  attribute.  Traced functions inherit the DEBUG and RETURN
                     traps from the calling shell.  The trace attribute has no  special  meaning  for  vari-ables. variables.
                     ables.
              -x     Mark names for export to subsequent commands via the environment.

              Using  `+'  instead of `-' turns off the attribute instead, with the exception that +a may not
              be used to destroy an array variable.  When used in a function, makes each name local, as with
              the local command.  If a variable name is followed by =value, the value of the variable is set
              to value.  The return value is 0 unless an invalid option is encountered, an attempt  is  made
              to  define a function using ``-f foo=bar'', an attempt is made to assign a value to a readonly
              variable, an attempt is made to assign a value to an array variable without using the compound
              assignment  syntax (see Arrays above), one of the names is not a valid shell variable name, an
              attempt is made to turn off readonly status for a readonly variable, an  attempt  is  made  to
              turn  off  array status for an array variable, or an attempt is made to display a non-existent
              function with -f.

       dirs [-clpv] [+n] [-n]
              Without options, displays the list of currently remembered directories.  The  default  display
              is  on  a  single line with directory names separated by spaces.  Directories are added to the
              list with the pushd command; the popd command removes entries from the list.
              +n     Displays the nth entry counting from the left of the list shown by  dirs  when  invoked
                     without options, starting with zero.
              -n     Displays  the  nth entry counting from the right of the list shown by dirs when invoked
                     without options, starting with zero.
              -c     Clears the directory stack by deleting all of the entries.
              -l     Produces a longer listing; the default listing format uses a tilde to denote  the  home
                     directory.
              -p     Print the directory stack with one entry per line.
              -v     Print  the directory stack with one entry per line, prefixing each entry with its index
                     in the stack.

              The return value is 0 unless an invalid option is supplied or n indexes beyond the end of  the
              directory stack.

       disown [-ar] [-h] [jobspec ...]
              Without  options,  each jobspec is removed from the table of active jobs.  If the -h option is
              given, each jobspec is not removed from the table, but is marked so that SIGHUP is not sent to
              the  job if the shell receives a SIGHUP.  If no jobspec is present, and neither the -a nor the
              -r option is supplied, the current job is used.  If no jobspec  is  supplied,  the  -a  option
              means to remove or mark all jobs; the -r option without a jobspec argument restricts operation
              to running jobs.  The return value is 0 unless a jobspec does not specify a valid job.

       echo [-neE] [arg ...]
              Output the args, separated by spaces, followed by a newline.  The return status is  always  0.
              If  -n is specified, the trailing newline is suppressed.  If the -e option is given, interpre-tation interpretation
              tation of the following backslash-escaped characters is enabled.  The -E option  disables  the
              interpretation  of  these  escape  characters,  even  on systems where they are interpreted by
              default.  The xpg_echo shell option may be used to dynamically determine whether or  not  echo
              expands  these  escape  characters  by default.  echo does not interpret -- to mean the end of
              options.  echo interprets the following escape sequences:
              \a     alert (bell)
              \b     backspace
              \c     suppress trailing newline
              \e     an escape character
              \f     form feed
              \n     new line
              \r     carriage return
              \t     horizontal tab
              \v     vertical tab
              \\     backslash
              \0nnn  the eight-bit character whose value is the octal value nnn (zero to three octal digits)
              \xHH   the eight-bit character whose value is the hexadecimal value HH (one or two hex digits)

       enable [-adnps] [-f filename] [name ...]
              Enable and disable builtin shell commands.  Disabling a builtin allows a  disk  command  which
              has  the  same name as a shell builtin to be executed without specifying a full pathname, even
              though the shell normally searches for builtins before disk commands.  If  -n  is  used,  each
              name is disabled; otherwise, names are enabled.  For example, to use the test binary found via
              the PATH instead of the shell builtin version, run ``enable -n test''.  The -f option means to
              load the new builtin command name from shared object filename, on systems that support dynamic
              loading.  The -d option will delete a builtin previously loaded with -f.  If no name arguments
              are  given,  or  if  the  -p option is supplied, a list of shell builtins is printed.  With no
              other option arguments, the list consists of all enabled shell builtins.  If -n  is  supplied,
              only  disabled  builtins  are  printed.   If  -a  is  supplied,  the list printed includes all
              builtins, with an indication of whether or not each is enabled.  If -s is supplied, the output
              is  restricted  to  the  POSIX special builtins.  The return value is 0 unless a name is not a
              shell builtin or there is an error loading a new builtin from a shared object.

       eval [arg ...]
              The args are read and concatenated together into a single command.  This command is then  read
              and executed by the shell, and its exit status is returned as the value of eval.  If there are
              no args, or only null arguments, eval returns 0.

       exec [-cl] [-a name] [command [arguments]]
              If command is specified, it replaces the shell.  No new process  is  created.   The  arguments
              become the arguments to command.  If the -l option is supplied, the shell places a dash at the
              beginning of the zeroth arg passed to command.  This is what login(1)  does.   The  -c  option
              causes  command to be executed with an empty environment.  If -a is supplied, the shell passes
              name as the zeroth argument to the executed command.  If command cannot be executed  for  some
              reason,  a  non-interactive shell exits, unless the shell option execfail is enabled, in which
              case it returns failure.  An interactive shell returns failure if the file cannot be executed.
              If command is not specified, any redirections take effect in the current shell, and the return
              status is 0.  If there is a redirection error, the return status is 1.

       exit [n]
              Cause the shell to exit with a status of n.  If n is omitted, the exit status is that  of  the
              last command executed.  A trap on EXIT is executed before the shell terminates.

       export [-fn] [name[=word]] ...
       export -p
              The supplied names are marked for automatic export to the environment of subsequently executed
              commands.  If the -f option is given, the names refer to functions.  If no names are given, or
              if  the -p option is supplied, a list of all names that are exported in this shell is printed.
              The -n option causes the export property to be removed from each name.  If a variable name  is
              followed by =word, the value of the variable is set to word.  export returns an exit status of
              0 unless an invalid option is encountered, one of the names is  not  a  valid  shell  variable
              name, or -f is supplied with a name that is not a function.

       fc [-e ename] [-nlr] [first] [last]
       fc -s [pat=rep] [cmd]
              Fix  Command.   In the first form, a range of commands from first to last is selected from the
              history list.  First and last may be specified as a string (to locate the last command  begin-ning beginning
              ning with that string) or as a number (an index into the history list, where a negative number
              is used as an offset from the current command number).  If last is not specified it is set  to
              the  current  command  for  listing (so that ``fc -l -10'' prints the last 10 commands) and to
              first otherwise.  If first is not specified it is set to the previous command for editing  and
              -16 for listing.

              The  -n  option suppresses the command numbers when listing.  The -r option reverses the order
              of the commands.  If the -l option is given, the commands are listed on standard output.  Oth-erwise, Otherwise,
              erwise, the editor given by ename is invoked on a file containing those commands.  If ename is
              not given, the value of the FCEDIT variable is used, and the value of EDITOR if FCEDIT is  not
              set.   If  neither variable is set, vi is used.  When editing is complete, the edited commands
              are echoed and executed.

              In the second form, command is re-executed after each instance of pat is replaced by  rep.   A
              useful  alias to use with this is ``r="fc -s"'', so that typing ``r cc'' runs the last command
              beginning with ``cc'' and typing ``r'' re-executes the last command.

              If the first form is used, the return value is 0 unless an invalid option  is  encountered  or
              first  or  last  specify history lines out of range.  If the -e option is supplied, the return
              value is the value of the last command executed or failure if an error occurs with the  tempo-rary temporary
              rary  file  of commands.  If the second form is used, the return status is that of the command
              re-executed, unless cmd does not specify a valid history line, in which case fc returns  fail-ure. failure.
              ure.

       fg [jobspec]
              Resume jobspec in the foreground, and make it the current job.  If jobspec is not present, the
              shell's notion of the current job is used.  The return value is that  of  the  command  placed
              into the foreground, or failure if run when job control is disabled or, when run with job con-trol control
              trol enabled, if jobspec does not specify a valid job or jobspec  specifies  a  job  that  was
              started without job control.

       getopts optstring name [args]
              getopts  is  used  by shell procedures to parse positional parameters.  optstring contains the
              option characters to be recognized; if a character is followed  by  a  colon,  the  option  is
              expected to have an argument, which should be separated from it by white space.  The colon and
              question mark characters may not be used as option  characters.   Each  time  it  is  invoked,
              getopts  places  the  next option in the shell variable name, initializing name if it does not
              exist, and the index of the next argument to be processed into the variable OPTIND.  OPTIND is
              initialized to 1 each time the shell or a shell script is invoked.  When an option requires an
              argument, getopts places that argument into the variable OPTARG.  The  shell  does  not  reset
              OPTIND  automatically;  it must be manually reset between multiple calls to getopts within the
              same shell invocation if a new set of parameters is to be used.

              When the end of options is encountered, getopts exits with a return value greater  than  zero.
              OPTIND is set to the index of the first non-option argument, and name is set to ?.

              getopts  normally  parses  the positional parameters, but if more arguments are given in args,
              getopts parses those instead.

              getopts can report errors in two ways.  If the first character of optstring is a colon, silent
              error  reporting  is  used.   In normal operation diagnostic messages are printed when invalid
              options or missing option arguments are encountered.  If the variable OPTERR is set to  0,  no
              error messages will be displayed, even if the first character of optstring is not a colon.

              If  an  invalid option is seen, getopts places ? into name and, if not silent, prints an error
              message and unsets OPTARG.  If getopts is silent, the option  character  found  is  placed  in
              OPTARG and no diagnostic message is printed.

              If  a required argument is not found, and getopts is not silent, a question mark (?) is placed
              in name, OPTARG is unset, and a diagnostic message is printed.  If getopts is silent,  then  a
              colon (:) is placed in name and OPTARG is set to the option character found.

              getopts  returns  true  if an option, specified or unspecified, is found.  It returns false if
              the end of options is encountered or an error occurs.

       hash [-lr] [-p filename] [-dt] [name]
              For each name, the full file name of the command is determined by searching the directories in
              $PATH and remembered.  If the -p option is supplied, no path search is performed, and filename
              is used as the full file name of the command.  The -r option causes the shell  to  forget  all
              remembered  locations.   The  -d  option causes the shell to forget the remembered location of
              each name.  If the -t option is supplied, the full pathname to which each name corresponds  is
              printed.   If  multiple  name  arguments  are supplied with -t, the name is printed before the
              hashed full pathname.  The -l option causes output to be displayed in a  format  that  may  be
              reused  as  input.   If  no  arguments are given, or if only -l is supplied, information about
              remembered commands is printed.  The return status is true unless a name is not  found  or  an
              invalid option is supplied.

       help [-s] [pattern]
              Display  helpful  information  about  builtin  commands.   If pattern is specified, help gives
              detailed help on all commands matching pattern; otherwise help for all the builtins and  shell
              control  structures  is printed.  The -s option restricts the information displayed to a short
              usage synopsis.  The return status is 0 unless no command matches pattern.

       history [n]
       history -c
       history -d offset
       history -anrw [filename]
       history -p arg [arg ...]
       history -s arg [arg ...]
              With no options, display the command history list with line numbers.  Lines listed  with  a  *
              have  been  modified.   An  argument  of n lists only the last n lines.  If the shell variable
              HISTTIMEFORMAT is set and not null, it is used as a format string for strftime(3)  to  display
              the  time stamp associated with each displayed history entry.  No intervening blank is printed
              between the formatted time stamp and the history line.  If filename is supplied, it is used as
              the  name  of  the history file; if not, the value of HISTFILE is used.  Options, if supplied,
              have the following meanings:
              -c     Clear the history list by deleting all the entries.
              -d offset
                     Delete the history entry at position offset.
              -a     Append the ``new'' history lines (history lines entered since the beginning of the cur-rent current
                     rent bash session) to the history file.
              -n     Read  the history lines not already read from the history file into the current history
                     list.  These are lines appended to the history file since the beginning of the  current
                     bash session.
              -r     Read the contents of the history file and use them as the current history.
              -w     Write the current history to the history file, overwriting the history file's contents.
              -p     Perform history substitution on the following args and display the result on the  stan-dard standard
                     dard  output.  Does not store the results in the history list.  Each arg must be quoted
                     to disable normal history expansion.
              -s     Store the args in the history list as a single entry.  The last command in the  history
                     list is removed before the args are added.

              If the HISTTIMEFORMAT is set, the time stamp information associated with each history entry is
              written to the history file.  The return value is 0 unless an invalid option  is  encountered,
              an error occurs while reading or writing the history file, an invalid offset is supplied as an
              argument to -d, or the history expansion supplied as an argument to -p fails.

       jobs [-lnprs] [ jobspec ... ]
       jobs -x command [ args ... ]
              The first form lists the active jobs.  The options have the following meanings:
              -l     List process IDs in addition to the normal information.
              -p     List only the process ID of the job's process group leader.
              -n     Display information only about jobs that have changed status since the  user  was  last
                     notified of their status.
              -r     Restrict output to running jobs.
              -s     Restrict output to stopped jobs.

              If jobspec is given, output is restricted to information about that job.  The return status is
              0 unless an invalid option is encountered or an invalid jobspec is supplied.

              If the -x option is supplied, jobs replaces any jobspec found in command or args with the cor-responding corresponding
              responding  process group ID, and executes command passing it args, returning its exit status.

       kill [-s sigspec | -n signum | -sigspec] [pid | jobspec] ...
       kill -l [sigspec | exit_status]
              Send the signal named by sigspec or signum to the processes named by pid or jobspec.   sigspec
              is either a case-insensitive signal name such as SIGKILL (with or without the SIG prefix) or a
              signal number; signum is a signal number.  If sigspec is not present, then SIGTERM is assumed.
              An argument of -l lists the signal names.  If any arguments are supplied when -l is given, the
              names of the signals corresponding to the arguments are listed, and the return  status  is  0.
              The  exit_status argument to -l is a number specifying either a signal number or the exit sta-tus status
              tus of a process terminated by a signal.  kill returns true if at least one  signal  was  suc-cessfully successfully
              cessfully sent, or false if an error occurs or an invalid option is encountered.

       let arg [arg ...]
              Each arg is an arithmetic expression to be evaluated (see ARITHMETIC EVALUATION).  If the last
              arg evaluates to 0, let returns 1; 0 is returned otherwise.

       local [option] [name[=value] ...]
              For each argument, a local variable named name is created, and assigned value.  The option can
              be  any  of  the options accepted by declare.  When local is used within a function, it causes
              the variable name to have a visible scope restricted to that function and its children.   With
              no operands, local writes a list of local variables to the standard output.  It is an error to
              use local when not within a function.  The return status is 0 unless local is used  outside  a
              function, an invalid name is supplied, or name is a readonly variable.

       logout Exit a login shell.

       popd [-n] [+n] [-n]
              Removes  entries  from the directory stack.  With no arguments, removes the top directory from
              the stack, and performs a cd to the new top directory.  Arguments, if supplied, have the  fol-lowing following
              lowing meanings:
              +n     Removes  the  nth entry counting from the left of the list shown by dirs, starting with
                     zero.  For example: ``popd +0'' removes the first directory, ``popd +1'' the second.
              -n     Removes the nth entry counting from the right of the list shown by dirs, starting  with
                     zero.   For  example:  ``popd  -0'' removes the last directory, ``popd -1'' the next to
                     last.
              -n     Suppresses the normal change of directory when removing directories from the stack,  so
                     that only the stack is manipulated.

              If  the  popd  command is successful, a dirs is performed as well, and the return status is 0.
              popd returns false if an invalid option is encountered, the directory stack is empty,  a  non-existent nonexistent
              existent directory stack entry is specified, or the directory change fails.

       printf [-v var] format [arguments]
              Write  the  formatted  arguments  to the standard output under the control of the format.  The
              format is a character string which contains three types of objects:  plain  characters,  which
              are  simply  copied  to  standard  output, character escape sequences, which are converted and
              copied to the standard output, and format specifications, each of which causes printing of the
              next  successive argument.  In addition to the standard printf(1) formats, %b causes printf to
              expand backslash escape sequences in the corresponding argument  (except  that  \c  terminates
              output, backslashes in \', \", and \? are not removed, and octal escapes beginning with \0 may
              contain up to four digits), and %q causes printf to output the  corresponding  argument  in  a
              format that can be reused as shell input.

              The  -v  option causes the output to be assigned to the variable var rather than being printed
              to the standard output.

              The format is reused as necessary to consume all of the arguments.   If  the  format  requires
              more arguments than are supplied, the extra format specifications behave as if a zero value or
              null string, as appropriate, had been supplied.  The return value is zero on success, non-zero
              on failure.

       pushd [-n] [dir]
       pushd [-n] [+n] [-n]
              Adds  a  directory to the top of the directory stack, or rotates the stack, making the new top
              of the stack the current working directory.  With no arguments, exchanges the top two directo-ries directories
              ries  and  returns  0,  unless the directory stack is empty.  Arguments, if supplied, have the
              following meanings:
              +n     Rotates the stack so that the nth directory (counting from the left of the  list  shown
                     by dirs, starting with zero) is at the top.
              -n     Rotates  the stack so that the nth directory (counting from the right of the list shown
                     by dirs, starting with zero) is at the top.
              -n     Suppresses the normal change of directory when adding directories to the stack, so that
                     only the stack is manipulated.
              dir    Adds  dir  to  the directory stack at the top, making it the new current working direc-tory. directory.
                     tory.

              If the pushd command is successful, a dirs is performed as well.  If the first form  is  used,
              pushd  returns 0 unless the cd to dir fails.  With the second form, pushd returns 0 unless the
              directory stack is empty, a non-existent directory stack element is specified, or  the  direc-tory directory
              tory change to the specified new current directory fails.

       pwd [-LP]
              Print  the  absolute pathname of the current working directory.  The pathname printed contains
              no symbolic links if the -P option is supplied or the -o physical option to  the  set  builtin
              command  is  enabled.   If  the  -L  option is used, the pathname printed may contain symbolic
              links.  The return status is 0 unless an error occurs while reading the name  of  the  current
              directory or an invalid option is supplied.

       read [-ers] [-u fd] [-t timeout] [-a aname] [-p prompt] [-n nchars] [-d delim] [name ...]
              One  line is read from the standard input, or from the file descriptor fd supplied as an argu-ment argument
              ment to the -u option, and the first word is assigned to the first name, the  second  word  to
              the  second  name, and so on, with leftover words and their intervening separators assigned to
              the last name.  If there are fewer words read from the input stream than names, the  remaining
              names are assigned empty values.  The characters in IFS are used to split the line into words.
              The backslash character (\) may be used to remove any special meaning for the  next  character
              read and for line continuation.  Options, if supplied, have the following meanings:
              -a aname
                     The  words  are assigned to sequential indices of the array variable aname, starting at
                     0.  aname is unset before any new  values  are  assigned.   Other  name  arguments  are
                     ignored.
              -d delim
                     The  first character of delim is used to terminate the input line, rather than newline.
              -e     If the standard input is coming from a terminal, readline (see READLINE above) is  used
                     to obtain the line.
              -n nchars
                     read returns after reading nchars characters rather than waiting for a complete line of
                     input.
              -p prompt
                     Display prompt on standard error, without a trailing newline, before attempting to read
                     any input.  The prompt is displayed only if input is coming from a terminal.
              -r     Backslash  does not act as an escape character.  The backslash is considered to be part
                     of the line.  In particular, a backslash-newline pair may not be used as a line contin-uation. continuation.
                     uation.
              -s     Silent mode.  If input is coming from a terminal, characters are not echoed.
              -t timeout
                     Cause  read  to  time  out  and  return failure if a complete line of input is not read
                     within timeout seconds.  This option has no effect if read is not  reading  input  from
                     the terminal or a pipe.
              -u fd  Read input from file descriptor fd.

              If no names are supplied, the line read is assigned to the variable REPLY.  The return code is
              zero, unless end-of-file is encountered, read times out, or an invalid file descriptor is sup-plied supplied
              plied as the argument to -u.

       readonly [-apf] [name[=word] ...]
              The  given  names  are marked readonly; the values of these names may not be changed by subse-quent subsequent
              quent assignment.  If the -f option is supplied, the functions corresponding to the names  are
              so  marked.  The -a option restricts the variables to arrays.  If no name arguments are given,
              or if the -p option is supplied, a list of all readonly  names  is  printed.   The  -p  option
              causes  output to be displayed in a format that may be reused as input.  If a variable name is
              followed by =word, the value of the variable is set to word.  The return status is 0 unless an
              invalid  option  is encountered, one of the names is not a valid shell variable name, or -f is
              supplied with a name that is not a function.

       return [n]
              Causes a function to exit with the return value specified by n.  If n is omitted,  the  return
              status is that of the last command executed in the function body.  If used outside a function,
              but during execution of a script by the .  (source) command, it causes the shell to stop  exe-cuting executing
              cuting  that script and return either n or the exit status of the last command executed within
              the script as the exit status of the script.  If used outside a function and not during execu-tion execution
              tion  of  a  script  by ., the return status is false.  Any command associated with the RETURN
              trap is executed before execution resumes after the function or script.

       set [--abefhkmnptuvxBCHP] [-o option] [arg ...]
              Without options, the name and value of each shell variable are displayed in a format that  can
              be  reused as input for setting or resetting the currently-set variables.  Read-only variables
              cannot be reset.  In posix mode, only shell  variables  are  listed.   The  output  is  sorted
              according  to  the  current  locale.   When  options  are  specified,  they set or unset shell
              attributes.  Any arguments remaining after the options are processed are treated as values for
              the  positional parameters and are assigned, in order, to $1, $2, ...  $n.  Options, if speci-fied, specified,
              fied, have the following meanings:
              -a      Automatically mark variables and functions which are modified or created for export to
                      the environment of subsequent commands.
              -b      Report  the  status  of terminated background jobs immediately, rather than before the
                      next primary prompt.  This is effective only when job control is enabled.
              -e      Exit immediately if a simple command (see SHELL GRAMMAR above) exits with  a  non-zero
                      status.  The shell does not exit if the command that fails is part of the command list
                      immediately following a while or until keyword, part of the test in an  if  statement,
                      part  of a && or || list, or if the command's return value is being inverted via !.  A
                      trap on ERR, if set, is executed before the shell exits.
              -f      Disable pathname expansion.
              -h      Remember the location of commands as they  are  looked  up  for  execution.   This  is
                      enabled by default.
              -k      All arguments in the form of assignment statements are placed in the environment for a
                      command, not just those that precede the command name.
              -m      Monitor mode.  Job control is enabled.  This option is on by default  for  interactive
                      shells  on  systems that support it (see JOB CONTROL above).  Background processes run
                      in a separate process group and a line containing their exit status  is  printed  upon
                      their completion.
              -n      Read  commands  but do not execute them.  This may be used to check a shell script for
                      syntax errors.  This is ignored by interactive shells.
              -o option-name
                      The option-name can be one of the following:
                      allexport
                              Same as -a.
                      braceexpand
                              Same as -B.
                      emacs   Use an emacs-style command line editing interface.  This is enabled by default
                              when  the shell is interactive, unless the shell is started with the --noedit-ing --noediting
                              ing option.
                      errtrace
                              Same as -E.
                      functrace
                              Same as -T.
                      errexit Same as -e.
                      hashall Same as -h.
                      histexpand
                              Same as -H.
                      history Enable command history, as described above under HISTORY.  This option  is  on
                              by default in interactive shells.
                      ignoreeof
                              The  effect is as if the shell command ``IGNOREEOF=10'' had been executed (see
                              Shell Variables above).
                      keyword Same as -k.
                      monitor Same as -m.
                      noclobber
                              Same as -C.
                      noexec  Same as -n.
                      noglob  Same as -f.  nolog Currently ignored.
                      notify  Same as -b.
                      nounset Same as -u.
                      onecmd  Same as -t.
                      physical
                              Same as -P.
                      pipefail
                              If set, the return value of a pipeline is the value of  the  last  (rightmost)
                              command  to  exit with a non-zero status, or zero if all commands in the pipe-line pipeline
                              line exit successfully.  This option is disabled by default.
                      posix   Change the behavior of bash where the default operation differs from the POSIX
                              standard to match the standard (posix mode).
                      privileged
                              Same as -p.
                      verbose Same as -v.
                      vi      Use a vi-style command line editing interface.
                      xtrace  Same as -x.
                      If  -o is supplied with no option-name, the values of the current options are printed.
                      If +o is supplied with no option-name, a series of set commands to recreate  the  cur-rent current
                      rent option settings is displayed on the standard output.
              -p      Turn  on  privileged  mode.   In  this mode, the $ENV and $BASH_ENV files are not pro-cessed, processed,
                      cessed, shell functions are not inherited from  the  environment,  and  the  SHELLOPTS
                      variable,  if it appears in the environment, is ignored.  If the shell is started with
                      the effective user (group) id not equal to the real user (group) id, and the -p option
                      is  not supplied, these actions are taken and the effective user id is set to the real
                      user id.  If the -p option is supplied at startup, the effective user id is not reset.
                      Turning  this option off causes the effective user and group ids to be set to the real
                      user and group ids.
              -t      Exit after reading and executing one command.
              -u      Treat unset variables as an error when performing parameter expansion.   If  expansion
                      is  attempted  on  an  unset  variable, the shell prints an error message, and, if not
                      interactive, exits with a non-zero status.
              -v      Print shell input lines as they are read.
              -x      After expanding each simple command, for command, case  command,  select  command,  or
                      arithmetic for command, display the expanded value of PS4, followed by the command and
                      its expanded arguments or associated word list.
              -B      The shell performs brace expansion  (see  Brace  Expansion  above).   This  is  on  by
                      default.
              -C      If  set,  bash  does not overwrite an existing file with the >, >&, and <> redirection
                      operators.  This may be overridden when creating output files by using the redirection
                      operator >| instead of >.
              -E      If  set,  any  trap on ERR is inherited by shell functions, command substitutions, and
                      commands executed in a subshell environment.  The ERR trap is normally  not  inherited
                      in such cases.
              -H      Enable  !  style history substitution.  This option is on by default when the shell is
                      interactive.
              -P      If set, the shell does not follow symbolic links when executing commands  such  as  cd
                      that  change  the current working directory.  It uses the physical directory structure
                      instead.  By default, bash follows the logical chain of  directories  when  performing
                      commands which change the current directory.
              -T      If  set,  any traps on DEBUG and RETURN are inherited by shell functions, command sub-stitutions, substitutions,
                      stitutions, and commands executed in a subshell environment.   The  DEBUG  and  RETURN
                      traps are normally not inherited in such cases.
              --      If  no arguments follow this option, then the positional parameters are unset.  Other-wise, Otherwise,
                      wise, the positional parameters are set to the args, even if some of them begin with a
                      -.
              -       Signal  the  end of options, cause all remaining args to be assigned to the positional
                      parameters.  The -x and -v options are turned off.  If there are no  args,  the  posi-tional positional
                      tional parameters remain unchanged.

              The  options  are  off  by default unless otherwise noted.  Using + rather than - causes these
              options to be turned off.  The options can also be specified as arguments to an invocation  of
              the  shell.   The current set of options may be found in $-.  The return status is always true
              unless an invalid option is encountered.

       shift [n]
              The positional parameters from n+1 ... are renamed to $1 ....  Parameters represented  by  the
              numbers  $#  down  to $#-n+1 are unset.  n must be a non-negative number less than or equal to
              $#.  If n is 0, no parameters are changed.  If n is not given, it is assumed to be 1.  If n is
              greater than $#, the positional parameters are not changed.  The return status is greater than
              zero if n is greater than $# or less than zero; otherwise 0.

       shopt [-pqsu] [-o] [optname ...]
              Toggle the values of variables controlling optional shell behavior.  With no options, or  with
              the  -p  option, a list of all settable options is displayed, with an indication of whether or
              not each is set.  The -p option causes output to be displayed in a form that may be reused  as
              input.  Other options have the following meanings:
              -s     Enable (set) each optname.
              -u     Disable (unset) each optname.
              -q     Suppresses  normal output (quiet mode); the return status indicates whether the optname
                     is set or unset.  If multiple optname arguments are given with -q, the return status is
                     zero if all optnames are enabled; non-zero otherwise.
              -o     Restricts  the  values  of  optname  to  be  those defined for the -o option to the set
                     builtin.

              If either -s or -u is used with no optname arguments, the display is limited to those  options
              which  are set or unset, respectively.  Unless otherwise noted, the shopt options are disabled
              (unset) by default.

              The return status when listing options is zero if all optnames are  enabled,  non-zero  other-wise. otherwise.
              wise.  When setting or unsetting options, the return status is zero unless an optname is not a
              valid shell option.

              The list of shopt options is:

              cdable_vars
                      If set, an argument to the cd builtin command that is not a directory is assumed to be
                      the name of a variable whose value is the directory to change to.
              cdspell If  set, minor errors in the spelling of a directory component in a cd command will be
                      corrected.  The errors checked for are transposed characters, a missing character, and
                      one character too many.  If a correction is found, the corrected file name is printed,
                      and the command proceeds.  This option is only used by interactive shells.
              checkhash
                      If set, bash checks that a command found in the hash table  exists  before  trying  to
                      execute  it.  If a hashed command no longer exists, a normal path search is performed.
              checkwinsize
                      If set, bash checks the window size after each command and, if necessary, updates  the
                      values of LINES and COLUMNS.
              cmdhist If set, bash attempts to save all lines of a multiple-line command in the same history
                      entry.  This allows easy re-editing of multi-line commands.
              compat31
                      If set, bash changes its behavior to that of version 3.1 with respect to quoted  argu-ments arguments
                      ments to the conditional command's =~ operator.
              dotglob If set, bash includes filenames beginning with a `.' in the results of pathname expan-sion. expansion.
                      sion.
              execfail
                      If set, a non-interactive shell will not exit if it cannot execute the file  specified
                      as  an  argument  to  the exec builtin command.  An interactive shell does not exit if
                      exec fails.
              expand_aliases
                      If set, aliases are expanded as described above under ALIASES.  This option is enabled
                      by default for interactive shells.
              extdebug
                      If set, behavior intended for use by debuggers is enabled:
                      1.     The  -F  option  to  the declare builtin displays the source file name and line
                             number corresponding to each function name supplied as an argument.
                      2.     If the command run by the DEBUG trap returns a non-zero value, the next command
                             is skipped and not executed.
                      3.     If  the  command  run  by the DEBUG trap returns a value of 2, and the shell is
                             executing in a subroutine (a shell function or a shell script executed by the .
                             or source builtins), a call to return is simulated.
                      4.     BASH_ARGC and BASH_ARGV are updated as described in their descriptions above.
                      5.     Function  tracing  is enabled:  command substitution, shell functions, and sub-shells subshells
                             shells invoked with ( command ) inherit the DEBUG and RETURN traps.
                      6.     Error tracing is enabled:  command substitution, shell functions, and subshells
                             invoked with ( command ) inherit the ERROR trap.
              extglob If  set,  the extended pattern matching features described above under Pathname Expan-sion Expansion
                      sion are enabled.
              extquote
                      If set, $'string' and $"string" quoting is performed  within  ${parameter}  expansions
                      enclosed in double quotes.  This option is enabled by default.
              failglob
                      If  set, patterns which fail to match filenames during pathname expansion result in an
                      expansion error.
              force_fignore
                      If set, the suffixes specified by the FIGNORE shell variable cause words to be ignored
                      when  performing  word completion even if the ignored words are the only possible com-pletions. completions.
                      pletions.  See SHELL VARIABLES above for a description of  FIGNORE.   This  option  is
                      enabled by default.
              gnu_errfmt
                      If set, shell error messages are written in the standard GNU error message format.
              histappend
                      If  set,  the  history list is appended to the file named by the value of the HISTFILE
                      variable when the shell exits, rather than overwriting the file.
              histreedit
                      If set, and readline is being used, a user is  given  the  opportunity  to  re-edit  a
                      failed history substitution.
              histverify
                      If  set, and readline is being used, the results of history substitution are not imme-diately immediately
                      diately passed to the shell parser.  Instead, the resulting line is  loaded  into  the
                      readline editing buffer, allowing further modification.
              hostcomplete
                      If  set,  and readline is being used, bash will attempt to perform hostname completion
                      when a word containing a @ is being completed (see Completing under  READLINE  above).
                      This is enabled by default.
              huponexit
                      If set, bash will send SIGHUP to all jobs when an interactive login shell exits.
              interactive_comments
                      If  set, allow a word beginning with # to cause that word and all remaining characters
                      on that line to be ignored in an interactive shell (see COMMENTS above).  This  option
                      is enabled by default.
              lithist If  set,  and the cmdhist option is enabled, multi-line commands are saved to the his-tory history
                      tory with embedded newlines rather than using semicolon separators where possible.
              login_shell
                      The shell sets this option if it is started as a login shell (see  INVOCATION  above).
                      The value may not be changed.
              mailwarn
                      If  set,  and  a  file that bash is checking for mail has been accessed since the last
                      time it was checked, the message ``The mail in mailfile has been read'' is  displayed.
              no_empty_cmd_completion
                      If  set, and readline is being used, bash will not attempt to search the PATH for pos-sible possible
                      sible completions when completion is attempted on an empty line.
              nocaseglob
                      If set, bash matches filenames in a case-insensitive fashion when performing  pathname
                      expansion (see Pathname Expansion above).
              nocasematch
                      If  set,  bash matches patterns in a case-insensitive fashion when performing matching
                      while executing case or [[ conditional commands.
              nullglob
                      If set, bash allows patterns which match no files (see Pathname  Expansion  above)  to
                      expand to a null string, rather than themselves.
              progcomp
                      If set, the programmable completion facilities (see Programmable Completion above) are
                      enabled.  This option is enabled by default.
              promptvars
                      If set, prompt strings undergo parameter expansion, command  substitution,  arithmetic
                      expansion,  and  quote  removal  after being expanded as described in PROMPTING above.
                      This option is enabled by default.
              restricted_shell
                      The shell sets this option if it is started in restricted mode (see  RESTRICTED  SHELL
                      below).   The  value may not be changed.  This is not reset when the startup files are
                      executed, allowing the startup files to discover whether or not a shell is restricted.
              shift_verbose
                      If  set,  the  shift  builtin prints an error message when the shift count exceeds the
                      number of positional parameters.
              sourcepath
                      If set, the source (.) builtin uses the value of PATH to find the directory containing
                      the file supplied as an argument.  This option is enabled by default.
              xpg_echo
                      If set, the echo builtin expands backslash-escape sequences by default.
       suspend [-f]
              Suspend  the  execution  of this shell until it receives a SIGCONT signal.  The -f option says
              not to complain if this is a login shell; just suspend anyway.  The return status is 0  unless
              the shell is a login shell and -f is not supplied, or if job control is not enabled.
       test expr
       [ expr ]
              Return  a  status  of  0  or 1 depending on the evaluation of the conditional expression expr.
              Each operator and operand must be a separate argument.  Expressions are composed of  the  pri-maries primaries
              maries  described  above under CONDITIONAL EXPRESSIONS.  test does not accept any options, nor
              does it accept and ignore an argument of -- as signifying the end of options.

              Expressions may be combined using the following  operators,  listed  in  decreasing  order  of
              precedence.
              ! expr True if expr is false.
              ( expr )
                     Returns the value of expr.  This may be used to override the normal precedence of oper-ators. operators.
                     ators.
              expr1 -a expr2
                     True if both expr1 and expr2 are true.
              expr1 -o expr2
                     True if either expr1 or expr2 is true.

              test and [ evaluate conditional expressions using a set of rules based on the number of  argu-ments. arguments.
              ments.

              0 arguments
                     The expression is false.
              1 argument
                     The expression is true if and only if the argument is not null.
              2 arguments
                     If  the  first argument is !, the expression is true if and only if the second argument
                     is null.  If the first argument is one of the unary conditional operators listed  above
                     under  CONDITIONAL  EXPRESSIONS,  the expression is true if the unary test is true.  If
                     the first argument is not a valid unary conditional operator, the expression is  false.
              3 arguments
                     If  the  second  argument is one of the binary conditional operators listed above under
                     CONDITIONAL EXPRESSIONS, the result of the expression is the result of the binary  test
                     using the first and third arguments as operands.  If the first argument is !, the value
                     is the negation of the two-argument test using the second and third arguments.  If  the
                     first argument is exactly ( and the third argument is exactly ), the result is the one-argument oneargument
                     argument test of the second argument.  Otherwise, the expression is false.  The -a  and
                     -o operators are considered binary operators in this case.
              4 arguments
                     If the first argument is !, the result is the negation of the three-argument expression
                     composed of the remaining arguments.  Otherwise, the expression is parsed and evaluated
                     according to precedence using the rules listed above.
              5 or more arguments
                     The  expression  is parsed and evaluated according to precedence using the rules listed
                     above.

       times  Print the accumulated user and system times for the shell  and  for  processes  run  from  the
              shell.  The return status is 0.

       trap [-lp] [[arg] sigspec ...]
              The  command arg is to be read and executed when the shell receives signal(s) sigspec.  If arg
              is absent (and there is a single sigspec) or -, each specified signal is reset to its original
              disposition (the value it had upon entrance to the shell).  If arg is the null string the sig-nal signal
              nal specified by each sigspec is ignored by the shell and by the commands it invokes.  If  arg
              is  not  present and -p has been supplied, then the trap commands associated with each sigspec
              are displayed.  If no arguments are supplied or if only -p is given, trap prints the  list  of
              commands  associated with each signal.  The -l option causes the shell to print a list of sig-nal signal
              nal names and their corresponding numbers.  Each sigspec is either a signal  name  defined  in
              <signal.h>,  or  a  signal  number.   Signal  names are case insensitive and the SIG prefix is
              optional.  If a sigspec is EXIT (0) the command arg is executed on exit from the shell.  If  a
              sigspec  is  DEBUG, the command arg is executed before every simple command, for command, case
              command, select command, every arithmetic for command, and before the first  command  executes
              in  a  shell  function  (see  SHELL  GRAMMAR above).  Refer to the description of the extdebug
              option to the shopt builtin for details of its effect on the DEBUG trap.  If a sigspec is ERR,
              the  command  arg is executed whenever a simple command has a non-zero exit status, subject to
              the following conditions.  The ERR trap is not executed if the failed command is part  of  the
              command  list immediately following a while or until keyword, part of the test in an if state-ment, statement,
              ment, part of a && or || list, or if the command's return  value  is  being  inverted  via  !.
              These  are the same conditions obeyed by the errexit option.  If a sigspec is RETURN, the com-mand command
              mand arg is executed each time a shell function or a script executed  with  the  .  or  source
              builtins  finishes  executing.   Signals  ignored upon entry to the shell cannot be trapped or
              reset.  Trapped signals that are not being ignored are reset to their  original  values  in  a
              child  process when it is created.  The return status is false if any sigspec is invalid; oth-erwise otherwise
              erwise trap returns true.

       type [-aftpP] name [name ...]
              With no options, indicate how each name would be interpreted if used as a  command  name.   If
              the -t option is used, type prints a string which is one of alias, keyword, function, builtin,
              or file if name is an alias, shell reserved word, function, builtin,  or  disk  file,  respec-tively. respectively.
              tively.   If  the  name  is not found, then nothing is printed, and an exit status of false is
              returned.  If the -p option is used, type either returns the name of the disk file that  would
              be executed if name were specified as a command name, or nothing if ``type -t name'' would not
              return file.  The -P option forces a PATH search for each name, even if ``type -t name'' would
              not  return  file.   If a command is hashed, -p and -P print the hashed value, not necessarily
              the file that appears first in PATH.  If the -a option is used, type prints all of the  places
              that  contain  an  executable named name.  This includes aliases and functions, if and only if
              the -p option is not also used.  The table of hashed commands is not consulted when using  -a.
              The  -f  option  suppresses  shell function lookup, as with the command builtin.  type returns
              true if any of the arguments are found, false if none are found.

       ulimit [-SHacdefilmnpqrstuvx [limit]]
              Provides control over the resources available to the shell and to processes started by it,  on
              systems that allow such control.  The -H and -S options specify that the hard or soft limit is
              set for the given resource.  A hard limit cannot be increased once it is set; a soft limit may
              be  increased  up to the value of the hard limit.  If neither -H nor -S is specified, both the
              soft and hard limits are set.  The value of limit can be a number in the  unit  specified  for
              the  resource  or one of the special values hard, soft, or unlimited, which stand for the cur-rent current
              rent hard limit, the current soft limit, and no limit, respectively.  If limit is omitted, the
              current  value  of  the  soft limit of the resource is printed, unless the -H option is given.
              When more than one resource is specified, the limit name  and  unit  are  printed  before  the
              value.  Other options are interpreted as follows:
              -a     All current limits are reported
              -c     The maximum size of core files created
              -d     The maximum size of a process's data segment
              -e     The maximum scheduling priority ("nice")
              -f     The maximum size of files written by the shell and its children
              -i     The maximum number of pending signals
              -l     The maximum size that may be locked into memory
              -m     The maximum resident set size
              -n     The maximum number of open file descriptors (most systems do not allow this value to be
                     set)
              -p     The pipe size in 512-byte blocks (this may not be set)
              -q     The maximum number of bytes in POSIX message queues
              -r     The maximum real-time scheduling priority
              -s     The maximum stack size
              -t     The maximum amount of cpu time in seconds
              -u     The maximum number of processes available to a single user
              -v     The maximum amount of virtual memory available to the shell
              -x     The maximum number of file locks

              If limit is given, it is the new value of the specified resource (the  -a  option  is  display
              only).  If no option is given, then -f is assumed.  Values are in 1024-byte increments, except
              for -t, which is in seconds, -p, which is in units of 512-byte blocks, and -n  and  -u,  which
              are unscaled values.  The return status is 0 unless an invalid option or argument is supplied,
              or an error occurs while setting a new limit.

       umask [-p] [-S] [mode]
              The user file-creation mask is set to mode.  If mode begins with a digit, it is interpreted as
              an  octal number; otherwise it is interpreted as a symbolic mode mask similar to that accepted
              by chmod(1).  If mode is omitted, the current value of the mask is  printed.   The  -S  option
              causes the mask to be printed in symbolic form; the default output is an octal number.  If the
              -p option is supplied, and mode is omitted, the output is in a form  that  may  be  reused  as
              input.  The return status is 0 if the mode was successfully changed or if no mode argument was
              supplied, and false otherwise.

       unalias [-a] [name ...]
              Remove each name from the list of defined aliases.  If -a is supplied, all  alias  definitions
              are removed.  The return value is true unless a supplied name is not a defined alias.

       unset [-fv] [name ...]
              For  each name, remove the corresponding variable or function.  If no options are supplied, or
              the -v option is given, each name refers to a shell variable.  Read-only variables may not  be
              unset.   If -f is specified, each name refers to a shell function, and the function definition
              is removed.  Each unset variable or function is removed from the environment passed to  subse-quent subsequent
              quent commands.  If any of RANDOM, SECONDS, LINENO, HISTCMD, FUNCNAME, GROUPS, or DIRSTACK are
              unset, they lose their special properties, even if they are subsequently reset.  The exit sta-tus status
              tus is true unless a name is readonly.

       wait [n ...]
              Wait for each specified process and return its termination status.  Each n may be a process ID
              or a job specification; if a job spec is given, all  processes  in  that  job's  pipeline  are
              waited  for.   If n is not given, all currently active child processes are waited for, and the
              return status is zero.  If n specifies a non-existent process or job,  the  return  status  is
              127.  Otherwise, the return status is the exit status of the last process or job waited for.

RESTRICTED SHELL
       If bash is started with the name rbash, or the -r option is supplied at invocation, the shell becomes
       restricted.  A restricted shell is used to set up an environment more controlled  than  the  standard
       shell.   It  behaves  identically to bash with the exception that the following are disallowed or not
       performed:

             changing directories with cd

             setting or unsetting the values of SHELL, PATH, ENV, or BASH_ENV

             specifying command names containing /

             specifying a file name containing a / as an argument to the .  builtin command

             Specifying a filename containing a slash as an argument to the -p option to the  hash  builtin
              command

             importing function definitions from the shell environment at startup

             parsing the value of SHELLOPTS from the shell environment at startup

             redirecting output using the >, >|, <>, >&, &>, and >> redirection operators

             using the exec builtin command to replace the shell with another command

             adding or deleting builtin commands with the -f and -d options to the enable builtin command

             Using the enable builtin command to enable disabled shell builtins

             specifying the -p option to the command builtin command

             turning off restricted mode with set +r or set +o restricted.

       These restrictions are enforced after any startup files are read.

       When  a  command  that is found to be a shell script is executed (see COMMAND EXECUTION above), rbash
       turns off any restrictions in the shell spawned to execute the script.

SEE ALSO
       Bash Reference Manual, Brian Fox and Chet Ramey
       The Gnu Readline Library, Brian Fox and Chet Ramey
       The Gnu History Library, Brian Fox and Chet Ramey
       Portable Operating System Interface (POSIX) Part 2: Shell and Utilities, IEEE
       sh(1), ksh(1), csh(1)
       emacs(1), vi(1)
       readline(3)

FILES
       /bin/bash
              The bash executable
       /etc/profile
              The systemwide initialization file, executed for login shells
       ~/.bash_profile
              The personal initialization file, executed for login shells
       ~/.bashrc
              The individual per-interactive-shell startup file
       ~/.bash_logout
              The individual login shell cleanup file, executed when a login shell exits
       ~/.inputrc
              Individual readline initialization file

AUTHORS
       Brian Fox, Free Software Foundation
       bfox@gnu.org

       Chet Ramey, Case Western Reserve University
       chet@po.cwru.edu

BUG REPORTS
       If you find a bug in bash, you should report it.  But first, you should make sure that it really is a
       bug,  and that it appears in the latest version of bash.  The latest version is always available from
       ftp://ftp.gnu.org/pub/bash/.

       Once you have determined that a bug actually exists, use the bashbug command to submit a bug  report.
       If  you  have  a  fix,  you are encouraged to mail that as well!  Suggestions and `philosophical' bug
       reports may be mailed to bug-bash@gnu.org or posted to the Usenet newsgroup gnu.bash.bug.

       ALL bug reports should include:

       The version number of bash
       The hardware and operating system
       The compiler used to compile
       A description of the bug behaviour
       A short script or `recipe' which exercises the bug

       bashbug inserts the first three items automatically into the template it provides for  filing  a  bug
       report.

       Comments and bug reports concerning this manual page should be directed to chet@po.cwru.edu.

BUGS
       It's too big and too slow.

       There  are some subtle differences between bash and traditional versions of sh, mostly because of the
       POSIX specification.

       Aliases are confusing in some uses.

       Shell builtin commands and functions are not stoppable/restartable.

       Compound commands and command sequences of the form `a ; b ;  c'  are  not  handled  gracefully  when
       process  suspension is attempted.  When a process is stopped, the shell immediately executes the next
       command in the sequence.  It suffices to place the sequence of commands between parentheses to  force
       it into a subshell, which may be stopped as a unit.

       Commands  inside of $(...) command substitution are not parsed until substitution is attempted.  This
       will delay error reporting until some time after the command  is  entered.   For  example,  unmatched
       parentheses,  even  inside shell comments, will result in error messages while the construct is being
       read.

       Array variables may not (yet) be exported.



GNU Bash-3.2                                  2006 September 28                                      BASH(1)

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