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(flex.info.gz) Introduction

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 3 Introduction
 **************
 
 `flex' is a tool for generating "scanners".  A scanner is a program
 which recognizes lexical patterns in text.  The `flex' program 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 "rules".
 `flex' generates as output a C source file, `lex.yy.c' by default,
 which defines a routine `yylex()'.  This file can be compiled and
 linked with the flex runtime 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.
 
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