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. The pgrep utility, for instance, displays the processes whose names match a given regular expression. Other commands contain the word "grep" to indicate they are search tools, typically ones that rely on regular expression matches. Binaries of these variants persist in most modern systems, usually linking to grep however, using these binaries has been deprecated in favor of using the -E and -F command-line switches of grep instead. The " fgrep" variant searches for any of a list of fixed strings using the Aho–Corasick string matching algorithm. The " egrep" variant supports an extended regular expression syntax added by Alfred Aho after Ken Thompson's original regular expression implementation. Early variants included egrep and fgrep, introduced in Version 7 Unix.
#Ksh grep output file software#
Root:x:0:0:root:/root:/bin/bash operator:x:11:0:operator:/root:/sbin/nologin $ grep -n root /etc/passwdġ:root:x:0:0:root:/root:/bin/bash 12:operator:x:11:0:operator:/root:/sbin/nologin $ grep -c false /etc/passwdĪ variety of grep implementations are available in many operating systems and software development environments. The following example demonstrates the output of the grep command given different arguments Stating that it is "generally cited as the prototypical software tool", McIlroy credited grep with "irrevocably ingraining" Thompson's tools philosophy in Unix. grep was first included in Version 4 Unix. He chose the name because in ed, the command g/re/p would print all lines matching a specified pattern.
#Ksh grep output file code#
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. McMahon analyze the text of the Federalist Papers to determine authorship of the individual papers. Thompson wrote the first version in PDP-11 assembly language to help Lee E. Thompson's account may explain the belief that grep was written overnight. The next day he presented the program to McIlroy, who said it was exactly what he wanted. Responding that he would think about such a utility overnight, Thompson actually corrected bugs and made improvements for about an hour. Doug McIlroy, unaware of its existence, asked Thompson to write such a program. Before it was named, grep was a private utility written by Ken Thompson to search files for certain patterns.
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