JOIN(1plan9)                                                      JOIN(1plan9)

       join - relational database operator

       join [ options ] file1 file2

       Join forms, on the standard output, a join of the two relations
       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 ASCII collating sequence
       on the fields on which they are to be joined, normally 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.

              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

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

       sort /etc/passwd | join -t: -1 1 -a 1 -e "" - bdays
              Add birthdays to the /etc/passwd file, leaving unknown birthdays
              empty.  The layout of /adm/users is given in passwd(5); bdays
              contains sorted lines like

       tr : ' ' </etc/passwd | 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 userids.


       sort(1), comm(1), awk(1)

       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.