Uniq

uniq
Original authorsKen Thompson
(AT&T Bell Laboratories)
DevelopersVarious open-source and commercial developers
ReleaseFebruary 1973; 53 years ago (1973-02)
Written inC
Operating systemUnix, Unix-like, Plan 9, Inferno, MSX-DOS, IBM i
PlatformCross-platform
TypeCommand
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, 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.

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

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

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

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

See also

References

  1. ↑ McIlroy, M. D. (1987). A Research Unix reader: annotated excerpts from the Programmer's Manual, 1971–1986 (PDF) (Technical report). CSTR. Bell Labs. 139.
  2. ↑ uniq – Shell and Utilities Reference, The Single UNIX Specification, Version 5 from The Open Group
  3. ↑ uniq(1) – Linux General Commands Manual from ManKier.com
  4. ↑ MSX-DOS2 Tools User's Manual by ASCII Corporation
  5. ↑ "CoreUtils for Windows". Archived from the original on 2025-07-30. Retrieved 2026-02-03.
  6. ↑ "Native Win32 ports of some GNU utilities". Archived from the original on 2006-02-09. Retrieved 2026-02-03.
  7. ↑ IBM. "IBM System i Version 7.2 Programming Qshell" (PDF). IBM. Archived (PDF) from the original on 2020-09-18. Retrieved 2020-09-05.