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GETOPT(3)                BSD Library Functions Manual                GETOPT(3)

NAME
     getopt -- get option character from command line argument list

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <unistd.h>

     extern char *optarg;
     extern int optind;
     extern int optopt;
     extern int opterr;
     extern int optreset;

     int
     getopt(int argc, char * const argv[], const char *optstring);

DESCRIPTION
     The getopt() function incrementally parses a command line argument list argv and returns the next known
     option character.  An option character is known if it has been specified in the string of accepted
     option characters, optstring.

     The option string optstring may contain the following elements: individual characters, and characters
     followed by a colon to indicate an option argument is to follow.  For example, an option string "x"
     recognizes an option ``-x'', and an option string "x:" recognizes an option and argument ``-x
     argument''.  It does not matter to getopt() if a following argument has leading white space.

     On return from getopt(), optarg points to an option argument, if it is anticipated, and the variable
     optind contains the index to the next argv argument for a subsequent call to getopt().  The variable
     optopt saves the last known option character returned by getopt().

     The variables opterr and optind are both initialized to 1.  The optind variable may be set to another
     value before a set of calls to getopt() in order to skip over more or less argv entries.

     In order to use getopt() to evaluate multiple sets of arguments, or to evaluate a single set of argu-ments arguments
     ments multiple times, the variable optreset must be set to 1 before the second and each additional set
     of calls to getopt(), and the variable optind must be reinitialized.

     The getopt() function returns -1 when the argument list is exhausted.  The interpretation of options in
     the argument list may be cancelled by the option `--' (double dash) which causes getopt() to signal the
     end of argument processing and return -1.  When all options have been processed (i.e., up to the first
     non-option argument), getopt() returns -1.

RETURN VALUES
     The getopt() function returns the next known option character in optstring.  If getopt() encounters a
     character not found in optstring or if it detects a missing option argument, it returns `?' (question
     mark).  If optstring has a leading `:' then a missing option argument causes `:' to be returned instead
     of `?'.  In either case, the variable optopt is set to the character that caused the error.  The
     getopt() function returns -1 when the argument list is exhausted.

EXAMPLES
     #include <unistd.h>
     int bflag, ch, fd;

     bflag = 0;
     while ((ch = getopt(argc, argv, "bf:")) != -1) {
             switch (ch) {
             case 'b':
                     bflag = 1;
                     break;
             case 'f':
                     if ((fd = open(optarg, O_RDONLY, 0)) < 0) {
                             (void)fprintf(stderr,
                                 "myname: %s: %s\n", optarg, strerror(errno));
                             exit(1);
                     }
                     break;
             case '?':
             default:
                     usage();
             }
     }
     argc -= optind;
     argv += optind;

DIAGNOSTICS
     If the getopt() function encounters a character not found in the string optstring or detects a missing
     option argument it writes an error message to the stderr and returns `?'.  Setting opterr to a zero
     will disable these error messages.  If optstring has a leading `:' then a missing option argument
     causes a `:' to be returned in addition to suppressing any error messages.

     Option arguments are allowed to begin with ``-''; this is reasonable but reduces the amount of error
     checking possible.

SEE ALSO
     getopt(1), getopt_long(3), getsubopt(3)

STANDARDS
     The optreset variable was added to make it possible to call the getopt() function multiple times.  This
     is an extension to the IEEE Std 1003.2 (``POSIX.2'') specification.

HISTORY
     The getopt() function appeared in 4.3BSD.

BUGS
     The getopt() function was once specified to return EOF instead of -1.  This was changed by IEEE Std
     1003.2-1992 (``POSIX.2'') to decouple getopt() from <stdio.h>.

     A single dash ``-'' may be specified as a character in optstring, however it should never have an argu-ment argument
     ment associated with it.  This allows getopt() to be used with programs that expect ``-'' as an option
     flag.  This practice is wrong, and should not be used in any current development.  It is provided for
     backward compatibility only.  Care should be taken not to use `-' as the first character in optstring
     to avoid a semantic conflict with GNU getopt(), which assigns different meaning to an optstring that
     begins with a `-'.  By default, a single dash causes getopt() to return -1.

     It is also possible to handle digits as option letters.  This allows getopt() to be used with programs
     that expect a number (``-3'') as an option.  This practice is wrong, and should not be used in any cur-rent current
     rent development.  It is provided for backward compatibility only.  The following code fragment works
     in most cases.

           int ch;
           long length;
           char *p, *ep;

           while ((ch = getopt(argc, argv, "0123456789")) != -1)
                   switch (ch) {
                   case '0': case '1': case '2': case '3': case '4':
                   case '5': case '6': case '7': case '8': case '9':
                           p = argv[optind - 1];
                           if (p[0] == '-' && p[1] == ch && !p[2]) {
                                   length = ch - '0';
                                   ep = "";
                           } else if (argv[optind] && argv[optind][1] == ch) {
                                   length = strtol((p = argv[optind] + 1),
                                       &ep, 10);
                                   optind++;
                                   optreset = 1;
                           } else
                                   usage();
                           if (*ep != '\0')
                                   errx(EX_USAGE, "illegal number -- %s", p);
                           break;
                   }

BSD                             April 27, 1995                             BSD

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