Regexps are one of Perl's strongest features, but they're also one of the causes of Perl's greatest criticism: that it looks like line noise.

If you've ever had to examine someone else's regexp, or worse debug one, you'll probably agree that there's some merit in that criticism.

It doesn't have to be that way however, there's some simple steps you can take to make your regexps more readable and more maintainable, and this week we look at one of them: the /x modifier.

Continuing from my previous article "Anchoring Regexps", another common regexp mistake I see is use of * where the author really meant +.

So today I cover + and *: what's the difference and why does it matter?

A common mistake I find whenever I look at someone else's regexps, is a failure to anchor the regexp.

This is often, in my experience, the single biggest thing you can do to improve the performance of a regexp: it's one of those things you should learn to do in every regexp where applicable, which should be almost every regexp unless you're specifically looking for "something somewhere in the middle but I don't know where".

So, what is anchoring, and why does it have such a big impact?