This article is about the command-line utility. For other uses, see Uniq (disambiguation).
uniq
AuthorKen Thompson
(AT&T Bell Laboratories)
DeveloperVarious open-source and commercial developers
ReleasedFebruary 1973 (age 53)
Programming languageC
Operating systemUnix, Unix-like, Plan 9, Inferno, MSX-DOS, IBM i
PlatformCross-platform
GenreCommand
Licensecoreutils: GPLv3+
Plan 9: MIT License
Websiteman7.org/linux/man-pages/man1/uniq.1.html

uniq is a utility command on Unix, Plan 9, Inferno, and Unix-like operating systems which, when fed a text file or standard input, outputs the text with adjacent identical lines collapsed to one, unique line of text.

Overview

The command is a kind of filter program. Typically it is used after sort. It can also output only the duplicate lines (with the -d option), or add the number of occurrences of each line (with the -c option). For example, the following command lists the unique lines in a file, sorted by the number of times each occurs:

$ sort file | uniq -c | sort -n

Using uniq like this is common when building pipelines in shell scripts.

History

First appearing in Version 3 Unix,[1] uniq is now available for a number of different Unix and Unix-like operating systems. It is part of the X/Open Portability Guide since issue 2 of 1987. It was inherited into the first version of POSIX and the Single Unix Specification.[2]

The version bundled in GNU coreutils was written by Richard Stallman and David MacKenzie.[3]

A uniq command is also part of ASCII's MSX-DOS2 Tools for MSX-DOS version 2.[4]

The command is available as a separate package for Microsoft Windows as part of the GnuWin32 project[5] and the UnxUtils collection of native Win32 ports of common GNU Unix-like utilities.[6]

The uniq command has also been ported to the IBM i operating system.[7]

See also

References

  1. ^ McIlroy, M. D. (1987). A Research Unix reader: annotated excerpts from the Programmer's Manual, 1971–1986. No. 139. CSTR. Bell Labs.
  2. ^
  3. ^
  4. ^ MSX-DOS2 Tools User's Manual by ASCII Corporation
  5. ^ "CoreUtils for Windows". Archived 2025-07-30 at the Wayback Machine. Retrieved 2026-02-03.
  6. ^ "Native Win32 ports of some GNU utilities". Archived 2006-02-09 at the Wayback Machine. Retrieved 2026-02-03.
  7. ^ IBM. "IBM System i Version 7.2 Programming Qshell". IBM. Archived 2020-09-18 at the Wayback Machine. Retrieved 2020-09-05.