Can we use lex with regular expression variable

Question

Can I pass a pattern as an argument when I run the file using lex something similar to grep. Iam trying to implement grep using lex.

%{
      #include <stdio.h>
      char *pattern;
%}
%%
.*{pattern}.*   printf("%s\n",yytext);
%%
int yywrap()
{
    return 1;
}
int main(int argc,char *argv[])
{
  if(argc<3)
  {
    printf("usage:lexgrep pattern filename\n");
    exit(0);
  }
  pattern=argv[1];
  yyin=fopen(argv[2],"r");
  yylex();
  return 0;
}

This is what I tried. But it didn't worked out. Any suggestions?

Answer 1

No, the pattern(s) that lex recognizes are specified at compile time, not run time. To interpret patterns at run time, you'll need to build your own state machine on the fly.