As far as I can tell, those two regexes are identical: one as a plain match, and one as a substitution.
I'm guessing somebody is first testing to see if anything is found, and if it does, replace it.
Don't do that. Just plain s/// is enough, it won't do anything if nothing is found, so it's safe.

And if it happens to be the case that the existence of a match is used to conditionally control more than just a substitution, the  s/// operator returns the number of substitutions done, or false if there is no match, so it works just fine as a conditional expression. See s/PATTERN/REPLACEMENT/msixpogce in perlop. 

>perl -wMstrict -le
"my $str = 'foo';
 ;;
 if ($str =~ s{ foo }{bar}xms) {
   print qq{substituted with $str};
   }
"
substituted with bar

[download]

In reply to Re^2: Regular expression Problem by AnomalousMonk
in thread Regular expression Problem by archimca

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.