You didn't say in what way the code is behaving differently from your expectation but it's a fairly simple problem to solve correctly; even without recursion.

#!/usr/bin/perl -w
use strict;
use warnings;
use Data::Dumper;

my $length = 2;

my @motif = ( '' );

for my $i ( 1 .. $length ) {
    @motif = map {
        my $motif = $_;
        map $motif . $_, qw( a t c g );
    } @motif;
}

print Dumper \@motif;

[download]

Ie we start out with a list with a single empty string and then on each round, we create four new strings for every string we already have.

(The shard-eyed will notice that this code does the same work as the recursive variant, only explicitly — well, and in different order.)

Makeshifts last the longest.

In reply to Re: Trying to construct all possible strings from 4 bases [ATCG] by Aristotle
in thread Trying to construct all possible strings from 4 bases [ATCG] by monkfan

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.