---
name: "join"
section: "1plan9"
platform: "linux"
package: "9base"
version: "1:6-14"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/join/1plan9"
---

# join(1plan9)

relational database operator

## 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 one of the file names 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 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*.

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*.

- **-1** *m*

  - **-2** *m*

  Join on the *m*th field of *file1* or *file2*.

- **-j***n m*

  Archaic equivalent for **-***n* **m***.*

- **-o***fields*

  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 designators.

- **-t***c*

  Use character *c* as the only separator (tab character) on input and output. Every appearance of *c* in a line is significant.

## EXAMPLES

- sort /etc/passwd \| join -t: -1 1 -a 1 -e "" - bdays

  Add birthdays to the **/etc/passwd** file, leaving unknown birthdays empty. The layout of  **/adm/users** is given in [*passwd*(5)](/passwd/5.md); **bdays** contains sorted lines like

- tr : ' ' \</etc/passwd \| 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 userids.

## SOURCE

**/src/cmd/join.c**

## SEE ALSO

[*sort*(1)](/sort/1.md), [*comm*(1)](/comm/1.md), [*awk*(1)](/awk/1.md)

## BUGS

With default field separation, the collating sequence is that of **sort -b** **-k***y***,***y;* with **-t**, the sequence is that of **sort -t***x* **-k***y***,***y.*

One of the files must be randomly accessible.