* 安裝bison/flex

sudo apt-get install flex

sudo yum install flex

* words.l

%option noyywrap
%{
int chars = 0;
int words = 0;
int lines = 0;
%}

%%
[a-zA-Z]+ { words++; chars += strlen(yytext); }
\n  { chars++; lines++; }
.   { chars++; }
%%

main(int argc, char **argv)
{
  if(argc > 1) {
    if(!(yyin = fopen(argv[1], "r"))) {
      perror(argv[1]);
      return (1);
    }
    yylex();
    printf("%8d%8d%8d\n", lines, words, chars);
  }
}
 

* compile

flex words.l
gcc lex.yy.c -o words

* run

./words /etc/passwd
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http://www.php-internals.com/book/?p=chapt02/02-03-01-lex-and-yacc