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From Wikipedia, the free encyclopedia
Original author(s)Ken Thompson
(AT&T Bell Laboratories)
Developer(s)Various open-source and commercial developers
Initial releaseFebruary 1973; 51 years ago (1973-02)
Written inC
Operating systemUnix, Unix-like, Plan 9, Inferno, MSX-DOS, IBM i
Licensecoreutils: GPLv3+
Plan 9: MIT License

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.


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.


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[edit]


  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 4 from The Open Group
  3. ^ uniq(1) – Linux General Commands Manual
  4. ^ MSX-DOS2 Tools User's Manual by ASCII Corporation
  5. ^ CoreUtils for Windows
  6. ^ Native Win32 ports of some GNU utilities
  7. ^ IBM. "IBM System i Version 7.2 Programming Qshell" (PDF). IBM. Retrieved 2020-09-05.

External links[edit]