grep is a command-line utility for searching plain-text data sets for lines that match a regular expression. Its name comes from the ed command g/re/p (globally search for a regular expression and print matching lines), which has the same effect.
grep was originally developed for the Unix operating system, but later available for all Unix-like systems and some others such as OS-9.
|Original author(s)||Ken Thompson|
|Developer(s)||AT&T Bell Laboratories|
|Initial release||November 1974|
|Platform||Unix, Unix-like, Plan 9, Inferno, OS-9, MSX-DOS, IBM i|
Before it was named, grep was a private utility written by Ken Thompson to search files for certain patterns. Doug McIlroy, unbeknown of its existence, asked Thompson to write such a program. Responding that he would think about such a utility overnight, Thompson actually corrected bugs and made improvements for about an hour. The next day he presented the program to McIlroy, who said it was exactly what he wanted. Thompson's account may explain the belief that grep was written overnight.
Thompson wrote the first version in PDP-11 assembly language to help Lee E. McMahon analyze the text of the Federalist Papers to determine authorship of the individual papers. The ed text editor (also authored by Thompson) had regular expression support but could not be used on such a large amount of text, so Thompson excerpted that code into a standalone tool. He chose the name because in ed, the command g/re/p would print all lines matching a specified pattern.
grep was first included in Version 4 Unix. Stating that it is "generally cited as the prototypical software tool", McIlroy credited
grep with "irrevocably ingraining" Thompson's tools philosophy in Unix.
The following example demonstrates the output of the
grep command given different arguments
$ grep root /etc/passwd root:x:0:0:root:/root:/bin/bash operator:x:11:0:operator:/root:/sbin/nologin $ grep -n root /etc/passwd 1:root:x:0:0:root:/root:/bin/bash 12:operator:x:11:0:operator:/root:/sbin/nologin $ grep -c false /etc/passwd 7
A variety of
grep implementations are available in many operating systems and software development environments. Early variants included
fgrep, introduced in Version 7 Unix. The "
egrep" variant supports an extended regular expression syntax added by Alfred Aho after Ken Thompson's original regular expression implementation. The "
fgrep" variant searches for any of a list of fixed strings using the Aho–Corasick string matching algorithm. Binaries of these variants persist in most modern systems, however their explicit usage has been deprecated and the functionalities of these variants are included in
grep as the command-line switches
-F; the use of the switches is therefore the recommended method of use.
Other commands contain the word "grep" to indicate that they search (usually for regular expression matches). The
pgrep utility, for instance, displays the processes whose names match a given regular expression.
In the Perl programming language, grep is the name of the built-in function that finds elements in a list that satisfy a certain property. This higher-order function is typically named filter in functional programming languages.
The software Adobe InDesign has functions GREP (since CS3 version (2007)), in the find/change dialog box "GREP" tab, and introduced with InDesign CS4 in paragraph styles "GREP styles".
agrep (approximate grep) matches even when the text only approximately fits the search pattern.
agrep -2 netmasks myfile
- will find "netmasks" but also any other word that can be derived from it , given no more than two substitutions.
agrep -B netmasks myfile
- (B for BEST) generates a list of matches with the closest (that is those with the fewest substitutions) listed first.
Usage as a verbEdit
In December 2003, the Oxford English Dictionary Online added draft entries for "grep" as both a noun and a verb.
A common verb usage is the phrase "You can't grep dead trees"—meaning one can more easily search through digital media, using tools such as
grep, than one could with a hard copy (i.e., one made from dead trees, paper). Compare with google.
- Boyer–Moore string search algorithm
- agrep, an approximate string-matching command
- find (Windows), a DOS and Windows command that performs text searches, similar to a simple
- find (Unix), a Unix command that finds files by attribute, very different from
- List of Unix commands
- vgrep, or "visual
- Kernighan, Brian (1984). The Unix Programming Environment. Prentice Hall. pp. 102. ISBN 0-13-937681-X.
- “grep was a private command of mine for quite a while before i made it public.” -Ken Thompson Archived 2015-05-26 at the Wayback Machine, By Benjamin Rualthanzauva, Published on Feb 5, 2014, Medium
- Hauben et al. 1997, Ch. 9
- Raymond, Eric. "grep". Jargon File. Archived from the original on 2006-06-17. Retrieved 2006-06-29.
- Paul S. Dayan (1992). The OS-9 Guru - 1 : The Facts. Galactic Industrial Limited. ISBN 0-9519228-0-7.
- VCF East 2019 -- Brian Kernighan interviews Ken Thompson (video). YouTube. 6 May 2019. (35 mins)
- Computerphile, Where GREP Came From, interview with Brian Kernighan
- "ed regexes". perl.plover.com. Archived from the original on 20 October 2017. Retrieved 24 April 2018.
- "How Grep Got its Name". robots.thoughtbot.com. Archived from the original on 9 August 2017. Retrieved 24 April 2018.
- McIlroy, M. D. (1987). A Research Unix reader: annotated excerpts from the Programmer's Manual, 1971–1986 (PDF) (Technical report). CSTR. Bell Labs. 139. Archived (PDF) from the original on 2017-11-11.
- Abou-Assaleh, Tony; Wei Ai (March 2004). Survey of Global Regular Expression Print (GREP) Tools (Technical report). Dalhousie University.
- Hume, Andrew (1988). "A Tale of Two Greps". Software—Practice & Experience. 18 (11): 1063. doi:10.1002/spe.4380181105.
- Meurant, Gerard (12 Sep 1990). Algorithms and Complexity. Elsevier Science. p. 278. ISBN 9780080933917. Archived from the original on 4 March 2016. Retrieved 12 December 2015.
- "grep". www.pubs.opengroup.org. The Open Group. Archived from the original on 28 November 2015. Retrieved 12 December 2015.
- "pgrep(1)". www.linux.die.net. Archived from the original on 22 December 2015. Retrieved 12 December 2015.
- "grep". www.perldoc.perl.org. Archived from the original on 7 December 2015. Retrieved 12 December 2015.
- "pcregrep man page". www.pcre.org. University of Cambridge. Archived from the original on 23 December 2015. Retrieved 12 December 2015.
- "grep(1)". www.linux.die.net. Archived from the original on 10 December 2015. Retrieved 12 December 2015.
- Spalding, George (2000). Windows 2000 administration. Network professional's library. Osborne/McGraw-Hill. pp. 634. ISBN 978-0-07-882582-8. Retrieved 2010-12-10.
QGREP.EXE[:] A similar tool to grep in UNIX, this tool can be used to search for a text string
- MSX-DOS2 Tools User's Manual by ASCII Corporation
- IBM. "IBM System i Version 7.2 Programming Qshell" (PDF). Retrieved 2020-09-05.
- "Review: Adobe InDesign CS3 - CreativePro.com". creativepro.com. 20 April 2007. Archived from the original on 5 January 2018. Retrieved 24 April 2018.
- "InDesign Help: find/change". Archived from the original on 2016-08-28. Retrieved 2016-08-12.
- "Archived copy". Archived from the original on 2017-09-24. Retrieved 2018-01-05.CS1 maint: archived copy as title (link)
- "InDesign Help: GREP styles". Archived from the original on 2016-08-28. Retrieved 2016-08-12.
- S. Lee Henry (June 1998). "Proper Searching". Sun Expert. pp. 35–26.
- Jargon File, article "Documentation"
- Alain Magloire (August 2000). Grep: Searching for a Pattern. Iuniverse Inc. ISBN 0-595-10039-2.
- Hume, Andrew Grep wars: The strategic search initiative. In Peter Collinson, editor, Proceedings of the EUUG Spring 88 Conference, pages 237–245, Buntingford, UK, 1988. European UNIX User Group.
- Michael Hauben; et al. (April 1997). Netizens: On the History and Impact of Usenet and the Internet (Perspectives). Wiley-IEEE Computer Society Press. ISBN 978-0-8186-7706-9.
|The Wikibook How To Search has a page on the topic of: grep|
- GNU Grep official website
- GNU Grep manual
- Plan 9 Programmer's Manual, Volume 1 –
- Inferno General commands Manual –
- "why GNU grep is fast" - implementation details from GNU grep's author.
- Network grep - A packet analyzer used to match patterns at the network layer
- Command Grep – 25 practical examples