join - relational database operator
join [ options ] file1 file2
Join forms, on the standard output, a join of the two relations speci‐
fied 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, normally the first in each
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 con‐
sists 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.
-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 -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
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.
SEE ALSOsort(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.