#! perl
use strict;
use warnings;

my $seq = 'AATGGTTTCTCCCATCTCTCCATCGGCATAAAAATACAGAATGATCTAACGAA';

# Adapted from the regex by stevieb
my $re =
qr{
    (                           # capture each sequence:
        ATG                     # - which begins with the codon ATG
        (?: [ACGT]{3} )*?       # - followed by the smallest number of codons
        (?: TAG | TAA | TGA )   # - and ending with the codon TAG, TAA, or TGA
    )
}x;

print "$1\n" while $seq =~ /$re/g;