#!/usr/bin/perl

use strict;
use warnings;

$/ = undef;     # slurp-mode for input, just in case
while ( <> ) {  # reads stdin or all file names in ARGV
    s/\s+//g;   # remove whitespace
    tr/ACGTacgt//d; # remove all acgt

    if ( length() ) { # anything left?
        print "$ARGV bad content: $_\n";
    } else {
        print "$ARGV all clean!\n";
    }
}