join [-a filenumber | -v filenumber] [-1 fieldnumber] 
 [-2 fieldnumber] [-o list] [-e string] [-t char] file1 file2

join [-a filenumber] [-j fieldnumber] [-j1 fieldnumber] 
 [-j2 fieldnumber] [-o list] [-e string] [-t char] file1 file2

The join command forms, on the standard output, a join of the two relations specified by the lines of file1 and file2.

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. This format can be changed by using the -o option (see below). The -a option can be used to add unmatched lines to the output. The -v option can be used to output only unmatched lines.

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.

If the input files are not in the appropriate collating sequence, the results are unspecified.

Some of the options below use the argument filenumber. This argument should be a 1 or a 2 referring to either file1 or file2, respectively.

-a filenumber

-e string

-j fieldnumber

-j1 fieldnumber

-j2 fieldnumber

-o list

-t char

-v filenumber

-1 fieldnumber

-2fieldnumber

The following operands are supported:

file1

file2

file1 and file2 must be sorted in increasing collating sequence as determined by LC_COLLATE on the fields on which they are to be joined, normally the first in each line (see sort(1)).

See largefile(5) for the description of the behavior of join when encountering files greater than or equal to 2 Gbyte (2^31 bytes).

Example 1 Joining the password file and group file

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.

example% join -j1 4-j2 3 -o 1.1 2.1 1.6 -t:/etc/passwd /etc/group

Example 2 Using the -o option

The -o 0 field essentially selects the union of the join fields. For example, given file phone:

!Name Phone Number
Don +1 123-456-7890
Hal +1 234-567-8901
Yasushi +2 345-678-9012

and file fax:

!Name Fax Number

Don +1 123-456-7899

Keith +1 456-789-0122

Yasushi +2 345-678-9011

where the large expanses of white space are meant to each represent a single tab character), the command:

example% join -t"tab" -a 1 -a 2 -e '(unknown)' -o 0,1.2,2.2 phone fax

would produce

!Name Phone Number Fax Number
Don +1 123-456-7890 +1 123-456-7899
Hal +1 234-567-8901 (unknown
Keith (unknown) +1 456-789-012
Yasushi +2 345-678-9012 +2 345-678-9011

See environ(5) for descriptions of the following environment variables that affect the execution of join: LANG, LC_ALL, LC_CTYPE, LC_MESSAGES, LC_COLLATE, and NLSPATH.

The following exit values are returned:

0

>0

See attributes(5) for descriptions of the following attributes:

awk(1), comm(1), sort(1), uniq(1), attributes(5), environ(5), largefile(5), standards(5)

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.