#!/usr/bin/perl -w

use strict;

open (INPUT_FILE, "$ARGV[0]") || die "can't open file: $!";
         
if ( <INPUT_FILE> =~ m/[^actgACTG\s]/ ) {
    print "File contains something besides actg sequence.\n";
} else {
    print "good!\n";
}            
      
close INPUT_FILE;