PHP regex: what is "class at offset 0"?

Question

I'm trying to strip all punctuation out of a string using a simple regular expression and the php preg_replace function, although I get the following error:

Compilation failed: POSIX named classes are supported only within a class at offset 0

I guess this means I can't use POSIX named classes outside of a class at offset 0. My question is, what does it means when it says "within a class at offset 0 "?

$string = "I like: perl";    

if (eregi('[[:punct:]]', $string))  
    $new = preg_replace('[[:punct:]]', ' ', $string); echo $new;

Answer 1

The preg_* functions expect Perl compatible regular expressions with delimiters. So try this:

preg_replace('/[[:punct:]]/', ' ', $string)

Answer 2

NOTE: The g modifier is not needed with PHP's PCRE implementation!

In addition to Gumbo's answer, use the g modifier to replace all occurances of punctuation:

preg_replace('/[[:punct:]]/g', ' ', $string)
//                         ^

From Johnathan Lonowski (see comments):

> [The g modifier] means "Global" -- i.e., find all existing matches. Without it, regex functions will stop searching after the first match.

Answer 3

An explanation of why you're getting that error: PCRE uses Perl's loose definition of what a delimiter is. Your outer []s look like valid delimiters to it, causing it to read [:punct:] as the regex part.

(Oh, and avoid the ereg functions if you can - they're not going to be included in PHP 5.3.)

Answer 4

I just added g to the regexp as suggested in one of the anwers, it did the opposite of wahts expected and DIDN'T filter out the punctuation, turns out preg_replace doesnt require g as it's global/recursive in the first place