Consider: 

#!/usr/bin/perl -w
use strict;
my $match= "hi";
my $re= qr/($match)/;
print "\$match is $match\n";
print "'chimp' matches (", 'chimp' =~ $re, ")\n";
$match= "lo";
print "\$match is $match\n";
print "'slow' matches (", 'slow' =~ $re, ")\n";
print "'chimp' matches (", 'chimp' =~ $re, ")\n";

[download]
produces 
$match is hi
'chimp' matches (hi)
$match is lo
'slow' matches ()
'chimp' matches (hi)

[download]
So why does the qr// operator support the /o option? It already appears to only compile the regex once even without /o.

        - tye (but my friends call me "Tye")

In reply to qr//o ... "o"?? by tye

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.