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Lex (software)
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<p>Lex is a <a href="/facts/Computer_program/e38jH9N9">computer program</a> that generates <a href="/facts/Lexical_analysis/T1JYWpIf">lexical analyzers</a> ("scanners" or "lexers"). It is commonly used with the <a href="/facts/Yacc/sXp5I7Tw">yacc</a> <a href="/facts/Parser_generator/Ud51JPrv">parser generator</a> and is the standard lexical analyzer generator on many <a href="/facts/Unix/0pNL2seI">Unix</a> and <a href="/facts/Unix-like/YAKrAxzd">Unix-like</a> systems. An equivalent tool is specified as part of the <a href="/facts/POSIX/mQkSt234">POSIX</a> standard. </p><p>Lex reads an input <a href="/facts/Stream_(computing)/2jtBAp0U">stream</a> specifying the lexical analyzer and writes <a href="/facts/Source_code/o9J6Jv23">source code</a> which implements the lexical analyzer in the <a href="/facts/C_(programming_language)/Ky2No763">C programming language</a>. </p><p>In addition to C, some old versions of Lex could generate a lexer in <a href="/facts/Ratfor/xY77EmUQ">Ratfor</a>. </p>