Editing Lex (software) (section)

{{Short description|Lexical analyzer generator}}
{{Infobox software
| name                   = Lex
| logo                   = 
| screenshot             = 
| screenshot size        = 
| caption                = 
| author                 = [[Mike Lesk]], [[Eric Schmidt]]
| developer              = 
| released               = {{Start date and age|1975}}
| latest release version = 
| latest release date    = 
| programming language   = [[C (programming language)|C]]
| operating system       = [[Unix]], [[Unix-like]], [[Plan 9 from Bell Labs|Plan 9]]
| platform               = [[Cross-platform]]
| genre                  = [[Command (computing)|Command]]
| license                = Plan 9: [[MIT License]]
| website                = 
}}

'''Lex''' is a [[computer program]] that generates [[lexical analysis|lexical analyzer]]s ("scanners" or "lexers").<ref>{{cite book |last1=Levine |first1=John R. | author-link1=John R. Levine |last2=Mason |first2=Tony |last3=Brown |first3=Doug |title=lex & yacc |pages=[https://archive.org/details/lexyacc00levi/page/1 1]–2 |publisher=[[O'Reilly Media|O'Reilly]] |year=1992 |edition=2 |isbn=1-56592-000-7 |url=https://archive.org/details/lexyacc00levi|url-access=registration }}</ref><ref>{{Cite book | last=Levine | first=John | author-link=John Levine | title =flex & bison | publisher=O'Reilly Media | date=August 2009 | page=304 | url=http://oreilly.com/catalog/9780596155988 | isbn=978-0-596-15597-1}}</ref> It is commonly used with the [[yacc]] [[parser generator]] and is the standard lexical analyzer generator on many [[Unix]] and [[Unix-like]] systems. An equivalent tool is specified as part of the [[POSIX]] standard.<ref>[https://pubs.opengroup.org/onlinepubs/9699919799/utilities/lex.html The Open Group Base Specifications Issue 7, 2018 edition § Shell & Utilities § Utilities § lex]</ref>

Lex reads an input [[stream (computing)|stream]] specifying the lexical analyzer and writes [[source code]] which implements the lexical analyzer in the [[C (programming language)|C programming language]].

In addition to C, some old versions of Lex could generate a lexer in [[Ratfor]].<ref>{{cite book|title=Lex & Yacc |url=https://archive.org/details/lexyacc00levi |url-access=registration |author1=John R. Levine |author2=John Mason |author3=Doug Brown |publisher=O'Reilly |date=1992 |isbn=9781565920002 }}</ref>