Description
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{fH3}Description{f}

{fCode}flex{f} is a tool for generating {fUnderline}scanners{f}: programs which
recognized lexical patterns in text.  {fCode}flex{f} reads the given
input files, or its standard input if no file names are
given, for a description of a scanner to generate.  The
description is in the form of pairs of regular expressions
and C code, called {fUnderline}rules{f}. {fCode}flex{f} generates as output a C
source file, {fCite}lex.yy.c{f}, which defines a routine {fEmphasis}yylex(){f}.
This file is compiled and linked with the {fEmphasis}-lfl{f} library to
produce an executable.  When the executable is run, it
analyzes its input for occurrences of the regular
expressions.  Whenever it finds one, it executes the
corresponding C code.

