Lex program for generating a lexer implementing word counting.

wc.l

%{
/* Example of Lex program to count words in a file. */
#include <stdio.h>
#include <stdlib.h>
/* Numbers of characters, words and lines */
int nchar = 0;
int nword = 0;
int nline = 0;
%}
%%
[a-zA-Z0-9]+    { nchar += strlen(yytext); nword++; }
\n              { nchar++; nline++; }
.               { nchar++; }
%%
int main(void)
{
    yylex();
    printf("%d chars, %d words, %d lines\n", nchar, nword, nline);
    return 0;
}

lex wc.l
gcc lex.yy.c -o wc-lfl
cat wc.l | ./wc