Question

What’s the appropriate Perl or Java regex to extract only the second line below? It should find the div tag containing the class=”matchthis” attribute.

<div>Do not match this</div>
<div class="matchthis">MATCH THIS</div>
<div class="unimportant">Do not match this</div>

Please do not tell me to use DOM/Soup/etc. I wonder if raw regex can solve the simple problem above (you’ll be awarded for the answer!). Yes I’m aware of this post so don’t even mention it.

Answer 1

As you already seem to know, using regular expressions to parse HTML is a bad idea.

In this specific case, I’m pretty sure all you really want is this:

<div class="lulz">(.*)<\/div>

Now, the more flexible you want to get, the more unreadable your regular expression will become. And this is the danger of trying to use regular expressions instead of a proper parser. For instance, say you want to allow for additional attributes besides class. A kind of functional regular expression for this might look like:

<div[^>]*class="[^\"]*lulz[^\"]*".*>(.*)<\/div>

Totally readable, right? (Also, almost certainly very wrong.)