I agree with tilly and Not_a_Number about keeping it simple but...

I find the following easier to understand. Of the alternatives I have seen for putting everything in the RE I find the following easier to understand.

m[
    ^
    (a*)
    (??{ 'b' x ( length($1) + 1 ) })
    $
]x and print "'$_'\n"
for qw[ ab abb abbb aabb aabbb aabbbb  xaabbby ];


'abb'
'aabbb'

[download]

Update: I mean easier to understand than the alternatives that have been proposed for putting everything into the RE, not easier to understand than separating the condition. I would do it as Not_a_Number suggested myself.

Update: Note that this solution is only correct for strings matching the pattern /^a+b+$/ and decides differently than the test in the original post for many of the broader set of strings matching /a+b+/ (e.g. "ababb", "babbb", "acabbb" and many others. It can only be made more correct by making it much more complicated, so really not worth pursuing.

In reply to Re: Integrating match counts into regex matching by ig
in thread Integrating match counts into regex matching by pat_mc

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.