#! perl
use strict;
use warnings;

while (my $dna = <DATA>)
{
    chomp $dna;
    print "\n\$dna = '$dna'\n";

    while ($dna =~ /(\w\w\w)*?TGA/g)
    {
        print 'Got a TGA stop codon at position ', pos $dna, 
              ', immediately following [', $1, "]\n";
    }
}

__DATA__
ATCGTTGAA
ATCGTTGAATGCAAATGACATGAC