Regular expression for string that starts with 'http://'

I need a regular expression that wi开发者_StackOverflowll match anything that starts with 'http://'.

Just look to see if the first 7 characters are "http://":

substr($url, 0, 7) == "http://"

There isn't any need for regular expressions here.

This will match everything up to the first whitespace: ^http://[^\s]*

This should do it: ^http://.*

So basically, if you want to match a URL in a string, use:

http://([-\w\.]+)+(:\d+)?(/([\w/_\.]*(\?\S+)?)?)?