my $string = quotemeta shift;
die "Not a valid nucleotide sequence" if $string =~ /[^AGTC]/;

##</code><code>##

my $string = "TGAT";
my @nts = map { 
    my $tmp = $string;
    substr $tmp, $_, 1, '.';
    $tmp;
    } (0 .. length ($string) -1);
my $groupings = join '|', @nts;

my $sample = "TGATTGGAATGTTAGAT";

while ( $sample =~ /($groupings)/go )
{
    print "Matched $1 ending at position ", pos $sample, "\n";
}


##</code><code>##

@_=qw;
Just another Perl hacker,;
;$_=q=print
"@_"= and eval;