There is much discussion about which is faster and better.
If you plan on someday advancing to PHP6 your decision is made. Otherwise:
The general consensus is that PCRE is the better all around solution, but if you have a specific page with a lot of traffic, and you don't need PHP6 it may be worth some testing.
For example, from the PHP manual comments:
Deprecating POSIX regex in PHP for
Perl searching is like substituting
wooden boards and brick for a house
with pre-fabricated rooms and walls.
Sure, you may be able to mix and match
some of the parts but it's a lot
easier to modify with all the pieces
laid out in front of you.
PCRE faster than POSIX RE? Not always.
In a recent search-engine project here
at Cynergi, I had a simple loop with a
few cute ereg_replace() functions that
took 3min to process data. I changed
that 10-line loop into a 100-line
hand-written code for replacement and
the loop now took 10s to process the
same data! This opened my eye to what
can IN SOME CASES be very slow
regular expressions. Lately I decided
to look into Perl-compatible regular
expressions (PCRE). Most pages claim
PCRE are faster than POSIX, but a few
claim otherwise. I decided on
bechmarks of my own. My first few
tests confirmed PCRE to be faster,
but... the results were slightly
different than others were getting, so
I decided to benchmark every case of
RE usage I had on a 8000-line secure
(and fast) Webmail project here at
Cynergi to check it out. The results?
Inconclusive! Sometimes PCRE are
faster (sometimes by a factor greater
than 100x faster!), but some other
times POSIX RE are faster (by a factor
of 2x). I still have to find a rule on
when are one or the other faster. It's
not only about search data size,
amount of data matched, or "RE
compilation time" which would show
when you repeated the function often:
one would
answered 2009-09-01T10:30:12.393