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JOIN(1)                   BSD General Commands Manual                  JOIN(1)

NAME
     join -- relational database operator

SYNOPSIS
     join [-a file_number | -v file_number] [-e string] [-o list] [-t char] [-1 field] [-2 field] file1
          file2

DESCRIPTION
     The join utility performs an ``equality join'' on the specified files and writes the result to the
     standard output.  The ``join field'' is the field in each file by which the files are compared.  The
     first field in each line is used by default.  There is one line in the output for each pair of lines in
     file1 and file2 which have identical join fields.  Each output line consists of the join field, the
     remaining fields from file1 and then the remaining fields from file2.

     The default field separators are tab and space characters.  In this case, multiple tabs and spaces
     count as a single field separator, and leading tabs and spaces are ignored.  The default output field
     separator is a single space character.

     Many of the options use file and field numbers.  Both file numbers and field numbers are 1 based, i.e.,
     the first file on the command line is file number 1 and the first field is field number 1.  The follow-ing following
     ing options are available:

     -a file_number
             In addition to the default output, produce a line for each unpairable line in file file_number.

     -e string
             Replace empty output fields with string.

     -o list
             The -o option specifies the fields that will be output from each file for each line with match-ing matching
             ing join fields.  Each element of list has the either the form `file_number.field', where
             file_number is a file number and field is a field number, or the form `0' (zero), representing
             the join field.  The elements of list must be either comma (`,') or whitespace separated.  (The
             latter requires quoting to protect it from the shell, or, a simpler approach is to use multiple
             -o options.)

     -t char
             Use character char as a field delimiter for both input and output.  Every occurrence of char in
             a line is significant.

     -v file_number
             Do not display the default output, but display a line for each unpairable line in file
             file_number.  The options -v 1 and -v 2 may be specified at the same time.

     -1 field
             Join on the field'th field of file 1.

     -2 field
             Join on the field'th field of file 2.

     When the default field delimiter characters are used, the files to be joined should be ordered in the
     collating sequence of sort(1), using the -b option, on the fields on which they are to be joined, oth-erwise otherwise
     erwise join may not report all field matches.  When the field delimiter characters are specified by the
     -t option, the collating sequence should be the same as sort(1) without the -b option.

     If one of the arguments file1 or file2 is ``-'', the standard input is used.

EXIT STATUS
     The join utility exits 0 on success, and >0 if an error occurs.

COMPATIBILITY
     For compatibility with historic versions of join, the following options are available:

     -a      In addition to the default output, produce a line for each unpairable line in both file 1 and
             file 2.

     -j1 field
             Join on the field'th field of file 1.

     -j2 field
             Join on the field'th field of file 2.

     -j field
             Join on the field'th field of both file 1 and file 2.

     -o list ...
             Historical implementations of join permitted multiple arguments to the -o option.  These argu-ments arguments
             ments were of the form `file_number.field_number' as described for the current -o option.  This
             has obvious difficulties in the presence of files named `1.2'.

     These options are available only so historic shell scripts do not require modification.  They should
     not be used in new code.

LEGACY DESCRIPTION
     The -e option causes a specified string to be substituted into empty fields, even if they are in the
     middle of a line.  In legacy mode, the substitution only takes place at the end of a line.

     Only documented options are allowed.  In legacy mode, some obsolete options are re-written into current
     options.

     For more information about legacy mode, see compat(5).

SEE ALSO
     awk(1), comm(1), paste(1), sort(1), uniq(1), compat(5)

STANDARDS
     The join command conforms to IEEE Std 1003.1-2001 (``POSIX.1'').

BSD                              July 5, 2004                              BSD

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