uniq
| Original author(s) | Ken Thompson |
|---|---|
| Developer(s) | AT&T Bell Laboratories |
| Initial release | February 1973 |
| Operating system | Unix and Unix-like, MSX-DOS |
| Type | Command |
| License | GNU GPL v3 |
| Website | man7 |
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.
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]
See also
References
- ^ McIlroy, M. D. (1987). A Research Unix reader: annotated excerpts from the Programmer's Manual, 1971–1986 (PDF) (Technical report). CSTR. Bell Labs. 139.
- ^ – Shell and Utilities Reference, The Single UNIX Specification, Version 4 from The Open Group
- ^ – Linux General Commands Manual
- ^ MSX-DOS2 Tools User's Manual by ASCII Corporation
External links
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