use warnings;
use strict;

my $usage = <<"EOT";
usage:
    perl $0 dna_datafile.name
EOT

die $usage unless @ARGV >= 1;

my $filename = $ARGV[0];

my $rx_dna = qr{ \b [ATCGatcg]+ \b }xms;

open my $filehandle, '<', $filename or die "opening '$filename': $!";

SEQ:
while (my $seq = <$filehandle>) {

    next SEQ unless my ($dna) = $seq =~ m{ \A ($rx_dna) \s* \z }xms;

    (my $revcom = reverse $dna) =~ tr/ACGTacgt/TGCAtgca/;

    print "dna -> reverse complement \n";
    print "'$dna' -> '$revcom' \n\n";

    }

close $filehandle or die "closing '$filename': $!";

exit;

# define any subroutines here #########################################