I have this regular expression:
([http://some.url.com/index.php?showtopic=\"]*)([0-9]+(?:\.[0-9]*)?)
its for extracting links to topics from forum
Now when i use it in my script
$url = "([http://some.url.com/index.php?showtopic=\"]*)([0-9]+(?:\.[0-9]*)?)";
preg_match_all spits: "Unknown modifier '('"
This is also the call to preg_match
preg_match_all($url, $str, $matches,PREG_OFFSET_CAPTURE,3);
Can anyone help me with this obviously stupid problem
You need to wrap your regular expression in delimiters. Any character that isn't a special PCRE metacharacter will do, so I'll use #:
$url = "#([http://some.url.com/index.php?showtopic=\"]*)([0-9]+(?:\.[0-9]*)?)#";
You can learn more about delimiters in the PHP manual section for PCRE delimiters.
PCRE requires delimiters that separate the actual regular expression from optional modifiers. With PHP you can use any non-alphanumeric, non-backslash, non-whitespace character and even delimiters that come in pairs (brackets).
In your case the leading ( is used as delimiter and the first corresponding closing ) marks the end of the regular expression; the rest is treated as modifiers:
([http://some.url.com/index.php?showtopic=\"]*)([0-9]+(?:\.[0-9]*)?)
^ ^
But the first character after the ending delimiter (() is not a valid modifier. That why the error message says Unknown modifier '('.
In most cases / is used as delimiter like in Perl. But that would require to escape each occurrence of / in the regular expression. So it’s a good choice to choose a delimiter that’s not in the regular expression. In your case you could use # like BoltClock suggested.
Oh, and by the way: A character class like [http://some.url.com/index.php?showtopic=\"] represents just one single character of the listed characters. So either h, t, p, :, /, etc. If you mean to express http://some.url.com/index.php?showtopic=" literally, use just http://some\.url\.com/index\.php\?showtopic=" (don’t forget to escape the meta characters).