BrowserUk,
I haven't read any of the other solutions but this is the first idea that popped into my head. I haven't really tested it nor is it without at least 1 assumption. 
#!/usr/bin/perl
use strict;
use warnings;

my @M = 'a' .. 'z';
my $N = 42; # Assumes N is > 2

my ($minus_1, $minus_2) = ($M[rand @M], $M[rand @M]);
my $str = $minus_1 . $minus_2;

for (1 .. $N - 2) {
    my $idx = rand @M;
    $idx = ($idx + (int(rand $#M) + 1)) % @M if $minus_1 eq $minus_2 &
+& $M[$idx] eq $minus_2;
    $str .= $M[$idx];
    ($minus_1, $minus_2) = ($minus_2, $M[$idx]);
}
print "$str\n";

[download]
Update: Now after reading the solutions, I realize mine is almost identical to ikegami's. I chose to use scalars to hold the value of the last two chars instead of the regex, but very similar indeed.

Update 2: I cleaned up the code a bit though the algorithm stayed the same. I also fixed the bugs as shown below.

Cheers - L~R

In reply to Re: Random data generation. by Limbic~Region
in thread Random data generation. by BrowserUk

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.