Just another way to do it without loops (kind of cheating): 
my $c=0;
s/ \(      (?{++$c})
 | \)      (?{--$c})
 | ([^()]+)
 /$1 if ($c==0)/gex;

[download]
If you match an open paren, increment a counter;
if you match a close paren, decrement it;
if you match a string of non-parens, capture it;
substitute whatever was captured back in if the counter is zero.

There is an "if", but it can be replaced by an "x" operator, if you're a stickler. Or you could rewrite the replacement as $c==0 and $1.

Another little variation that doesn't rely on the (?{}) construct: 

s{([()]*)([^()]+)}
 {$c += $1=~y/(// - $1=~y/)//;
  $2 x !$c
 }ge;

[download]
Match any parens followed by any non-parens;
Add the count of opens and subtract the count of closes from your counter;
Substitute the non-paren portion back in if the counter is zero.
We're not really tightening our belts, it just feels that way because we're getting fatter.

In reply to Re: regular expression parentheses remover by Roy Johnson
in thread regular expression paranthesis remover by Kanishka

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.