# phpman > man > COMM(1)

> **TLDR:** Select or reject lines common to two files. Both files must be sorted.
>
- Produce three tab-separated columns: lines only in first file, lines only in second file, and common lines:
  `comm {{file1}} {{file2}}`
- Print only lines common to both files:
  `comm -12 {{file1}} {{file2}}`
- Print only lines common to both files, reading one file from `stdin`:
  `cat {{file1}} | comm -12 - {{file2}}`
- Get lines only found in first file, saving the result to a third file:
  `comm -23 {{file1}} {{file2}} > {{file1_only}}`
- Print lines only found in second file, when the files aren't sorted:
  `comm -13 <(sort {{file1}}) <(sort {{file2}})`

*Source: tldr-pages*

---

[COMM(1)](https://www.chedong.com/phpMan.php/man/COMM/1/markdown)                                     User Commands                                    [COMM(1)](https://www.chedong.com/phpMan.php/man/COMM/1/markdown)



## NAME
       comm - compare two sorted files line by line

## SYNOPSIS
       **comm** [_OPTION_]... _FILE1_ _FILE2_

## DESCRIPTION
       Compare sorted files FILE1 and FILE2 line by line.

       When FILE1 or FILE2 (not both) is -, read standard input.

       With  no  options,  produce  three-column output.  Column one contains lines unique to FILE1,
       column two contains lines unique to FILE2, and column three contains  lines  common  to  both
       files.

### -1

### -2

### -3

### --check-order
              check that the input is correctly sorted, even if all input lines are pairable

### --nocheck-order
              do not check that the input is correctly sorted

       **--output-delimiter**=_STR_
              separate columns with STR

### --total
              output a summary

### -z --zero-terminated
              line delimiter is NUL, not newline

       **--help** display this help and exit

### --version
              output version information and exit

       Note, comparisons honor the rules specified by 'LC_COLLATE'.

## EXAMPLES
       comm -12 file1 file2
              Print only lines present in both file1 and file2.

       comm -3 file1 file2
              Print lines in file1 not in file2, and vice versa.

## AUTHOR
       Written by Richard M. Stallman and David MacKenzie.

## REPORTING BUGS
       GNU coreutils online help: <<https://www.gnu.org/software/coreutils/>>
       Report any translation bugs to <<https://translationproject.org/team/>>

## COPYRIGHT
       Copyright  ©  2020 Free Software Foundation, Inc.  License GPLv3+: GNU GPL version 3 or later
       <<https://gnu.org/licenses/gpl.html>>.
       This is free software: you are free to change and redistribute it.  There is NO WARRANTY,  to
       the extent permitted by law.

## SEE ALSO
       [join(1)](https://www.chedong.com/phpMan.php/man/join/1/markdown), [uniq(1)](https://www.chedong.com/phpMan.php/man/uniq/1/markdown)

       Full documentation <<https://www.gnu.org/software/coreutils/comm>>
       or available locally via: info '(coreutils) comm invocation'



GNU coreutils 8.32                          January 2026                                     [COMM(1)](https://www.chedong.com/phpMan.php/man/COMM/1/markdown)