Hi all,
I wonder if one of you regex gurus might be able to give me some advice
regarding the most efficiant way of writing a particular rule....
Let's say I want to use regex to search for the phrase "color:blue" within a
<span> tag as in the example below (just a made-up example for the sake of
this question):
<span style="border:0px; color:blue; font-size:small">
In this case, the "color:blue" part is preceeded by some other text
("border:0px") after the first quote mark, but that preceeding text could in
fact be anything, and I want to allow for the fact that it could be
anything.
I've read at http://www.regular-expressions.info that it's best to avoid
backtracking if possible because that is resource-intensive.
So one possible solution would be the following:
/style="(.(?!color))+.color:blue/
In other words, after the first " (quote mark) it looks for any character
NOT followed by the word "color", and repeats that with the + character,
until it gets to the actual word "color". I believe this results in no (or
almost no?) backtracking. But I'm not sure if it's resource-intensive
anyway, because of the negative lookahead - are negative lookaheads
particularly resource intensive, when compared to backtracking? Is one
preferable over the other?
An alternative solution would be this:
/style="[^>]+color:blue/
But this will certainly involve some backtracking, especially if there is
even more text after the "color:blue" but before the closing > character,
for example the "font-size:small" text.
So what do you think?! Which way is best, ie. most efficient or least
resource-intensive?
Cheers,
Jeremy
