Re: perl regex in php and multiple escape rules

On Tue, 14 Sep 2004 11:18:33 +0200, Christophe Chisogne <christophe@publicityweb.com> 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 > > -- > PHP General Mailing List (http://www.php.net/) > To unsubscribe, visit: http://www.php.net/unsub.php > > 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!