uniq is a Unix utility which, when fed a text file or STDIN, outputs the text with adjacent identical lines collapsed to one, unique line of text.

Original author(s)Ken Thompson
Developer(s)AT&T Bell Laboratories
Initial releaseFebruary 1973; 47 years ago (1973-02)
Operating systemUnix and Unix-like, MSX-DOS
LicenseGNU GPL v3


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. The version bundled in GNU coreutils was written by Richard Stallman and David MacKenzie.[2] A uniq command is also part of ASCII's MSX-DOS2 Tools for MSX-DOS version 2.[3]

See alsoEdit


  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. ^ https://linux.die.net/man/1/uniq
  3. ^ MSX-DOS2 Tools User's Manual by ASCII Corporation

External linksEdit