Easy question

[GIJoe]

Hi!

I`m recently working with regular expressions and have lots of things to replace by my likings, and here is my question -

Is it better to use several preg_match_all with small expressions or one preg_match_all containing one big regular expression ?

Which is faster ?

[ednark]

depends on the expression probably the big one
however since you are dealing with webpages any regular expression will be fast enough not to be noticed unless you are parsing a several meg file for some reason at which point you might want to consider looking at set_time_limit()

[GIJoe]

Yes, at this time there is:

• 5 preg_match_all`s (quite large, but there are few small ones also)
• 5 preg_replace`s (like above)
• 2 preg_match`s split into one large preg_match

What do you think about this ?

[GIJoe]

I did small test - here is what it brought me -

1 - 0.0009331 together 0.0003861
2 - 0.0008349 together 0.00038491
3 - 0.000826 together 0.00038911
4 - 0.000832 together 0.0003871

Which means the bigger the expression is, the slower it gets (as the 'benchmark' shows - above 4 times slower).

Am I right ? 🙂

[ednark]

im not sure what your number are from... but if you benchmarked it on your server and one method came out faster than congrats you figured it out

[GIJoe]

I just did simple time benchmarking on both expressions - and my previous reply was wrong, combined regular expressions are 2-3 times faster than seperate ones.

[ednark]

perl style regular expression are pretty fast...

if you ever tried to cobble togther complex regular expressions in say microdoft word, you will find their expression parser to be very very very inefficient

would you mind posting your benchmarking code for anyone else following this thread so they can try on their machines?

[GIJoe]

its really nothing special, I`m just measuring the elapsed time of both cases, nothing more 🙂