NAME

join − relational database operator

SYNOPSIS

join [ options ] file1 file2

DESCRIPTION

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 [see sort(1)]. 

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.

The default input field separators are blank, tab, or new-line.  In this case, multiple separators count as one field separator, and leading separators are ignored.  The default output field separator is a blank. 

Some of the options below use the argument n. This argument should be a 1 or a 2 referring to either file1 or file2, respectively. The following 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 with string s.

−jn m Join on the mth field of file n. If n is missing, use the mth field in each file. Fields are numbered starting with 1. 

−o list Each output line includes 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.  The common field is not printed unless specifically requested. 

−tc Use character c as a separator (tab character).  Every appearance of c in a line is significant.  The character c is used as the field separator for both input and output. 

EXAMPLE

The following command line will join the password file and the group file, matching on the numeric group ID, and outputting the login name, the group name and the login directory.  It is assumed that the files have been sorted in ASCII collating sequence on the group ID fields. 

join −j1 4 −j2 3 −o 1.1 2.1 1.6 −t: /etc/passwd /etc/group

SEE ALSO

awk(1), comm(1), sort(1), uniq(1). 

NOTES

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 the join, sort, comm, uniq, and awk commands are wildly incongruous. 

Filenames that are numeric may cause conflict when the -o option is used just before listing filenames. 

CX/UX User’s Reference Manual