一个Flex例子，用于生成显示行号的词法分析程序。flex linno.lex; gcc lex.yy.c -o lineno; cat file.txt | ./lineno;

lineno.flex

%option noyywrap
%{
/* a Lex program that adds line numbers
   to lines of text, printing the new text
   to the standard output
*/
#include <stdio.h>
int lineno = 1;

%}

line .*\n

%%

{line} {printf("%5d %s", lineno++,yytext);}

%%


int main()
{ 
    yylex(); 
    return 0;
}