Re: [PHP4BETA] preg_replace Q

On Thu, 20 Apr 2000, Cynic wrote: > Great, this is it. Many, many thanks, Andrei. Now only if I knew what the > hell is going on. The manual says you need to escape $ to prevent PHP from > taking it for 'endofstring'. But why do you need THREE backslashes to escape > it in the pattern? Because if you use only one backslash, then it lets PHP know that you don't want it to interpret $ in any special way and just want it to be passed to preg_replace() as is. Now, preg_replace() will receive just $, which means the end of the string. So, in order to make it work like you wanted, you need to have a \ in front of $ by the time it gets to preg_replace() and the way to do it is to have three backslashes. The first two result in a \ and the other two in $. > Also, only one backslash is used to mark a backreference on > http://www.php.net/manual/pcre.pattern.syntax.php. Is it > correct under certain > circumstances? What are these? That is a generic PCRE library manual. It was not written with PHP in mind and since it talks only about PCRE syntax, it mentions only that you need to escape $ with a backslash if you want to use it literally. > I've spent several hours reading the PCRE pages in PHP manual, and came across > assertions. Would it speed the replace process if I used lookbehind assertion > on the $? From what I've read on the Pattern Syntax page, it should look > something like (?:<=\$)(\w+)/e , but I'm not sure if this is even remotely > true, not to mention that it seems like there should actually be three > backslashes. No, lookbehind assertions are not necessary here. > Another issue: the way it is, the regexp will replace foo$bar with > foo$GLOBALS['bar'] which I think it shouldn't. Seems like this could be avoided > with \b. How do I use it? I didn't find an example of it's use, i. e. where in > the pattern it should be. Use \B, like this: "/\B\\\$(\w+)/" > And last, but not least, is there some kind of tutorial for PCRE somewhere? I am not aware of any tutorials specific to PHP's PCRE implementation, but there are some for Perl's regular expressions which are pretty much equivalent. > Mind you, I have zero experience with PERL, I just know it exists, and learning > something from documents where examples are either too trivial to teach me > something new or too complicated to understand is terribly frustrating. I understand. Unfortunately, I don't have enough time currently to write a full-fledged regular expression tutorial. -Andrei * The best source is the source code. *