Here’s a quick tip: if you do a simple

perl -Mre=debug -le'"some test data here" =~ /your regex here/'

[download]

on the command line, you will see a) how the regex engine compiles your pattern, including which optimisations it discovered to be applicable while compiling, and b) which steps it performs during actual matching, including which optimisations actually made a difference. (F.ex., seeing “Match rejected by optimizer” for input you want to reject is ideal, because it means the match failure was detected even before the engine was powered up.)

This is an invaluable aid in understanding the performance characteristics of different patterns, as you can see just what the engine is really doing.

Makeshifts last the longest.

In reply to Re: Regex, capturing variables vs. speed by Aristotle
in thread Regex, capturing variables vs. speed by albert

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.