JOIN(1)                                                   JOIN(1)

     NAME
          join - relational database operator

     SYNOPSIS
          join [ options ] file1 file2

     DESCRIPTION
          Join forms, on the standard output, a join of the two rela-
          tions specified by the lines of file1 and file2. If one of
          the file names is `-', the standard input is used.

          File1 and file2 must be sorted in increasing UTF collating
          sequence on the fields on which they are to be joined, nor-
          mally the first in each line.

          There is one line in the output for each pair of lines in
          file1 and file2 that have identical join fields.  The output
          line normally consists of the common field, then the rest of
          the line from file1, then the rest of the line from file2.

          Input fields are normally separated spaces or tabs; output
          fields by space.  In this case, multiple separators count as
          one, and leading separators are discarded.

          The following options are recognized, with POSIX syntax.

          -a n     In addition to the normal output, produce a line
                   for each unpairable line in file n, where n is 1 or
                   2.

          -v n     Like -a, omitting output for paired lines.

          -e s     Replace empty output fields by string s.

          -1 m
          -2 m     Join on the mth field of file1 or file2.

          -jn m    Archaic equivalent for -n m.

          -ofields Each output line comprises the designated fields.
                   The comma-separated field designators are either 0,
                   meaning the join field, or have the form n.m, where
                   n is a file number and m is a field number.
                   Archaic usage allows separate arguments for field
                   designators.

          -tc      Use character c as the only separator (tab charac-
                   ter) on input and output.  Every appearance of c in
                   a line is significant.

     JOIN(1)                                                   JOIN(1)

     EXAMPLES
          sort -t: +1 /adm/users | join -t: -1 2 -a 1 -e "" - bdays
               Add birthdays to the /adm/users file, leaving unknown
               birthdays empty.  The layout of /adm/users is given in
               users(6); bdays contains sorted lines like
               `ken:Feb 4, 1953'.

          awk -F: '$3 != ""' /adm/users | tr : ' ' | sort -k 3,3 >temp
          join -1 3 -2 3 -o 1.1,2.1 temp temp | awk '$1 < $2'
               Print all pairs of users with identical non-empty
               userids.

     SOURCE
          /sys/src/cmd/join.c

     SEE ALSO
          sort(1), comm(1), awk(1)

     BUGS
          With default field separation, the collating sequence is
          that of sort -b -ky,y; with -t, the sequence is that of sort
          -tx -ky,y.

          One of the files must be randomly accessible.