grep

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.[3][4] grep was originally developed for the Unix operating system, but later available for all Unix-like systems and some others such as OS-9.[5]

grep
Example of grep command
Original author(s)Ken Thompson[1][2]
Developer(s)AT&T Bell Laboratories
Initial releaseNovember 1974 (1974-11)[1]
PlatformUnix and Unix-like, OS-9, MSX-DOS
TypeCommand

History

Before it was named, grep was a private utility written by Ken Thompson to search files. He was approached by his manager, Doug McIlroy, who expressed interest in having a similar functionality implemented. Thompson responded that he would think about such a utility overnight, but what he did was actually fixing bugs and making improvements, which took about an hour. The next day Thompson presented grep to McIlroy, who said it was exactly what he wanted. Thompson's account may explain why it is believed that grep was written overnight.[6]

The first version of grep was written by Ken Thompson in PDP-11 assembly language to help Lee E. McMahon analyze the text of the Federalist Papers to determine authorship of the individual papers.[7] 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.[1] He chose the name because in ed, the command g/re/p would print all lines matching a specified pattern.[8][9] grep was first included in Version 4 Unix. Stating that it is "generally cited as the prototypical software tool", Doug McIlroy credited grep with "irrevocably ingraining" Thompson's tools philosophy in Unix.[10]

Sample usage

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

Variations

A variety of grep implementations are available in many operating systems and software development environments.[11] Early variants included egrep and fgrep, introduced in Version 7 Unix.[10] The "egrep" variant supports an extended regular expression syntax added by Alfred Aho after Ken Thompson's original regular expression implementation.[12] The "fgrep" variant searches for any of a list of fixed strings using the Aho–Corasick string matching algorithm.[13] 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 -E and -F; the use of the switches is therefore the recommended method of use.[14]

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.[15]

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.[16] This higher-order function is typically named filter in functional programming languages.

The pcregrep command is an implementation of grep that uses Perl regular expression syntax.[17] Similar functionality can be invoked in the GNU version of grep with the -P flag.[18]

Ports of grep (within Cygwin and GnuWin32, for example) also run under Microsoft Windows. Some versions of Windows feature the similar qgrep or findstr command.[19]

A grep command is also part of ASCII's MSX-DOS2 Tools for MSX-DOS version 2.[20]

The software Adobe InDesign has functions GREP (since CS3 version (2007)[21]), in the find/change dialog box[22] "GREP" tab, and introduced with InDesign CS4[23] in paragraph styles[24] "GREP styles".

Usage as a verb

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).[25] Compare with google.

See also
  • 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 grep
  • find (Unix), a Unix command that finds files by attribute, very different from grep
  • List of Unix commands
  • vgrep, or "visual grep"

References
  1. Kernighan, Brian (1984). The Unix Programming Environment. Prentice Hall. pp. 102. ISBN 0-13-937681-X.
  2. “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
  3. Hauben et al. 1997, Ch. 9
  4. Raymond, Eric. "grep". Jargon File. Archived from the original on 2006-06-17. Retrieved 2006-06-29.
  5. Paul S. Dayan (1992). The OS-9 Guru - 1 : The Facts. Galactic Industrial Limited. ISBN 0-9519228-0-7.
  6. VCF East 2019 -- Brian Kernighan interviews Ken Thompson (video). YouTube. 6 May 2019. (35 mins)
  7. Computerphile, Where GREP Came From, interview with Brian Kernighan
  8. "ed regexes". perl.plover.com. Archived from the original on 20 October 2017. Retrieved 24 April 2018.
  9. "How Grep Got its Name". robots.thoughtbot.com. Archived from the original on 9 August 2017. Retrieved 24 April 2018.
  10. 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.
  11. Abou-Assaleh, Tony; Wei Ai (March 2004). Survey of Global Regular Expression Print (GREP) Tools (Technical report). Dalhousie University.
  12. Hume, Andrew (1988). "A Tale of Two Greps". Software—Practice & Experience. 18 (11): 1063.
  13. Meurant, Gerard (12 Sep 1990). Algorithms and Complexity. Elsevier Science. p. 278. Archived from the original on 4 March 2016. Retrieved 12 December 2015.
  14. "grep". www.pubs.opengroup.org. The Open Group. Archived from the original on 28 November 2015. Retrieved 12 December 2015.
  15. "pgrep(1)". www.linux.die.net. Archived from the original on 22 December 2015. Retrieved 12 December 2015.
  16. "grep". www.perldoc.perl.org. Archived from the original on 7 December 2015. Retrieved 12 December 2015.
  17. "pcregrep man page". www.pcre.org. University of Cambridge. Archived from the original on 23 December 2015. Retrieved 12 December 2015.
  18. "grep(1)". www.linux.die.net. Archived from the original on 10 December 2015. Retrieved 12 December 2015.
  19. 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
  20. MSX-DOS2 Tools User's Manual by ASCII Corporation
  21. "Review: Adobe InDesign CS3 - CreativePro.com". creativepro.com. 20 April 2007. Archived from the original on 5 January 2018. Retrieved 24 April 2018.
  22. "InDesign Help: find/change". Archived from the original on 2016-08-28. Retrieved 2016-08-12.
  23. "Archived copy". Archived from the original on 2017-09-24. Retrieved 2018-01-05.CS1 maint: archived copy as title (link)
  24. "InDesign Help: GREP styles". Archived from the original on 2016-08-28. Retrieved 2016-08-12.
  25. Jargon File, article "Documentation"
Notes
  • 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.
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