AFAIR Perl caches the previous stringification of the regexp, and compares that against the stringification of the new pattern to determine whether it needs recompiling. The stringification of a compiled pattern always captures those outside flags that affect compile-time so as to make this (and interpolation) safe, that's why you see for example:

% perl -E 'say qr{foo}i'
(?^ui:foo)
%

[download]

The /g flag is not listed in the docs because it is not supported by qr{}:

% perl -E 'say qr{foo}g'
Unknown regexp modifier "/g" at -e line 1, near "say "
Execution of -e aborted due to compilation errors.
%

[download]

(I think that error message could probably be improved. Patches welcome. :)

In reply to Re^7: On the regex pattern variable to be inserted into another (which recompile???) by hv
in thread On the regex pattern variable to be inserted into another 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.