
Flex is a fast scanner generator, which is a part of UNIX tools.
You can access flex manual on UNIX machine.
%man flex
Or, for quick reference for flex,
% flex -h 

input: lexical rule.
output: lex.yy.c

Usage:

1. %make                      /* compile */

- Flex object file is generated.
 
2. %./flex err_file [options] input_file  /* run */

- The flex is modified from original flex program for testing. 
- To use flex, err_file name should be specified(any name is O.K).
- You can find input_file samples in the in_out directory.
  ---> ./in_out/exam_1[2,3].lex
- After executing flex, lex.yy.c is generated.

3. %cc lex.yy.c libfl.a -lfl 

	
4.1 %a.out < input >& output

- You can fnd input samples for a.out in the in_out directory.
  ---> ./in_out/tmp*

Or just give a.out and standard input.
4.2 %a.out 

