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 file1 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 iden-
tical 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.
Fields are normally separated by blank, tab or newline. In this case, multiple separators
count as one, and leading separators are discarded.
These options are recognized:
-an In addition to the normal output, produce a line for each unpairable line in file
n, where n is 1 or 2.
-e s Replace empty output fields by string s.
-jn m Join on the mth field of file n. If n is missing, use the mth field in each file.
Each output line comprises the fields specifed in list, each element of which has
the form n.m, where n is a file number and m is a field number.
-tc Use character c as a separator (tab character). Every appearance of c in a line is
sort(1), comm(1), awk(1)
With default field separation, the collating sequence is that of sort -b; with -t, the
sequence is that of a plain sort.
The conventions of join, sort, comm, uniq, look and awk(1) are wildly incongruous.