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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]
It has since been available in illumos and reimplemented for the Linux and BSDs (DragonFly BSD, FreeBSD, NetBSD, and OpenBSD). It searches for all the named processes that can be specified as extended regular expression patterns, and—by default—returns their process ID. Alternatives include pidof (finds process ID given a program name) and ps.
He later added this capability to the Unix editor ed, which eventually led to the popular search tool grep's use of regular expressions ("grep" is a word derived from the command for regular expression searching in the ed editor: g/re/p meaning "Global search for Regular Expression and Print matching lines"). [15]
Regular Expression Flavor Comparison – Detailed comparison of the most popular regular expression flavors; Regexp Syntax Summary; Online Regular Expression Testing – with support for Java, JavaScript, .Net, PHP, Python and Ruby; Implementing Regular Expressions – series of articles by Russ Cox, author of RE2; Regular Expression Engines
grep is a command-line utility for searching plain-text data sets for lines matching a regular expression and by default reporting matching lines on standard output. tree is a command-line utility that recursively lists files found in a directory tree, indenting the filenames according to their position in the file hierarchy.
agrep (approximate grep) is an open-source approximate string matching program, developed by Udi Manber and Sun Wu between 1988 and 1991, [1] for use with the Unix operating system. It was later ported to OS/2, DOS, and Windows.
Perl Compatible Regular Expressions (PCRE) is a library written in C, which implements a regular expression engine, inspired by the capabilities of the Perl programming language. Philip Hazel started writing PCRE in summer 1997. [ 3 ]
pkill (see pgrep) is a command-line utility initially written for use with the Solaris 7 operating system in 1998. It has since been reimplemented for Linux and some BSDs.. As with the kill and killall commands, pkill is used to send signals to processes.