#!/usr/bin/perl -w

use strict;

my $DNA;  
chomp ( $DNA = $ARGV[0] );
open ( INPUT_FILE, "$DNA" ) or die;
         
if ( <INPUT_FILE> =~ m/[^actgACTG]/ ) {
    print "File contains something besides actg sequence.\n";
} else {     
    print "good!\n";
}