On Tue, 14 Sep 2004 11:18:33 +0200, Christophe Chisogne
[EMAIL PROTECTED] wrote:
In a word:
I'm looking for more detailed information about preg_replace
(and other perl regex functions) than in the php manual,
specifically about different escape rules interaction.
In more words:
PHP has it's own way of escaping strings [2]
Ex \ within '' is '\' (or '\\' if at the end or before ' )
\ within is \ (or \\ if at the end or before )
So \\ can be written '\\\' or '' or \\\ or
and \\\ can be written '\' or '\\' (same with )
(rule 1)
Perl regex are powerfull and came with other escape rules [3]
Ex regex to match... is ...
\ /\\/
(newline) \n /\n/
(2 chars) \n /\\n/
(rule 2)
My problem is about preg_replace function, because it's entry in
the php manual [1] is not specific enough -- I mean, writing
a real specification seems impossible without more details
The 'pattern' argument is a string, but how does php proceed it?
I guess it first uses rule1 then rule2, ie php string escape rule
(for ' and \ ) then perl regex rule (via verbatim use in perlre C library?)
This mean that to match \n (the 2 chars), the perl re is \\n
so correct php pattern is '\\\n' or 'n' or \\\n or n.
(see comment 29-Mar-2004 05:46 on [1]). Is this right?
/me think using perl regex is easier in perl than in php ;-)
Is it the same for the 'replacement' argument?
Another comment (steven -a-t- acko dot net, 08-Feb-2004 12:45) says
To make this easier, the data in a backreference with /e is run through
addslashes() before being inserted in your replacement expression.
Is that user right?
Ok, I can try to guess answers to my questions by probing things.
But that didnt tell me if my guesses are wrong, or if what I guess
is exactly what php pcre functions are supposed to do
(not only now with php x.y.z but in the future too).
And I prefer specifications over guesses.
(think about ppl using alt attribute instead of title
on img html tags : they guessed wrong by not reading html spec)
In other words, is there some details about escape rules
in pcre php functions? I feel much better when I can use
a stable, reliable and precise API.
Christophe
[1] preg_replace in php manual
http://www.php.net/manual/en/function.preg-replace.php
[2] strings in php manual
http://www.php.net/manual/en/language.types.string.php
[3] pcre syntax in php manual
http://www.php.net/manual/en/reference.pcre.pattern.syntax.php
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It's all very easy, actually. You take the real regex, and convert
that to a php string.
for example:
to match the two chars \n, in perl you'd do:
/\\n/
php requires each slash to be slashed again, so you'd get
$regex = '/n/';
whenever you're in doubt, put the regex into a var, print that var and
if that what you get is exactly the regex you'd use in perl, you're
good. And yes, I do agree with anybody who'd state that it's a bit
confusing. Cuz it is!
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