Warning: preg_match() [function.preg-match]: No ending delimiter '^' found
/ is missing. preg_match('/pattern/',$string);
preg_match("/^http:\/\/[-0-9a-z\._]+.*$/i", trim( $url ));
As it has been said in other answers, you have to use delimiters arround the regex. You have also the possibility to use another character than / to avoid escaping them:
return preg_match("~^http://[-0-9a-z._]+.*$~i", trim( $url ));And you could use \w that is shortcut of [a-zA-Z0-9_]:
return preg_match("~^http://[-\w.]+.*$~", trim( $url ));
Your regex needs a delimiter around it, e.g. /
return preg_match("/^http:\/\/[-0-9a-z\._]+.*$/i", trim( $url ));This delimiter can be different characters but it must be the same before and after your regex. You could e.g. also do this
~regex~or
#regex#The advantage is, use a delimiter that you don't have inside the regex. If you use / as delimiter and want to match "/" you have to escape it inside the regex ///, if you change the delimiter you could do #/# to match a "/"