Uniq

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]

• List of Unix commands

The Wikibook Guide to Unix has a page on the topic of: Commands

• uniq(1) – Linux User Manual – User Commands
• uniq(1) – Plan 9 Programmer's Manual, Volume 1
• uniq(1) – Inferno General commands Manual
• SourceForge UnxUtils – Port of several GNU utilities to Windows