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://'.

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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.

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

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

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

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