What is happening is as it stands the regular expression is evaluating two characters at a time.Whereas the frame for the matches should be one character. A sloppy fix would be: 
while (<DATA>) {
   $i=0 while s/\|\|/\| \|/g; # repeats as many times as is necessary
   print;  
}
As joost rightly says the forward lookahead operation is probably the best way to go.
To make regexes easier to read try using the debug pragma:

use re 'debugcolor'

To get insight into how the regexes do what they do ;)

I'd love to find a solution using the 'c' modifier .. but then I'm not Abigail

--

Brother Frankus.

¤

In reply to Re: Regex Backtracking by frankus
in thread Regex Backtracking by Anonymous Monk

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.