join - relational database operator
join [-an] [-e s] [-o list] [-tc] 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
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
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.
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.
Each output line comprises the fields specified 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 significant.
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