Uniq

This article is about the command-line utility. For other uses, see Uniq (disambiguation).

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.

uniq
Original author(s)	Ken Thompson (AT&T Bell Laboratories)
Developer(s)	Various open-source and commercial developers
Initial release	February 1973; 52 years ago (1973-02)
Written in	C
Operating system	Unix, Unix-like, Plan 9, Inferno, MSX-DOS, IBM i
Platform	Cross-platform
Type	Command
License	coreutils: GPLv3+ Plan 9: MIT License
Website	man7.org/linux/man-pages/man1/uniq.1.html

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

• List of Unix commands