I came across this link which has a nice little example of a regex to achieve a good validation.

Below is a copy and paste of building the regex string from that site with brief explanations of what each part achieves.

// SCHEME
$urlregex = "^(https?|ftp)\:\/\/";

// USER AND PASS (optional)
$urlregex .= "([a-z0-9+!*(),;?&=\$_.-]+(\:[a-z0-9+!*(),;?&=\$_.-]+)?@)?";
// HOSTNAME OR IP
$urlregex .= "[a-z0-9+\$_-]+(\.[a-z0-9+\$_-]+)*";
// PORT (optional)
$urlregex .= "(\:[0-9]{2,5})?";
// PATH (optional)
$urlregex .= "(\/([a-z0-9+\$_-]\.?)+)*\/?";// GET Query (optional)
$urlregex .= "(\?[a-z+&\$_.-][a-z0-9;:@/&%=+\$_.-]*)?";// ANCHOR (optional)
$urlregex .= "(#[a-z_.-][a-z0-9+\$_.-]*)?\$";
This builds a nice regex string which can be used with the eregi() function to validate a url string like so:

if (eregi($urlregex, $url))
{
echo "URL Valid";
}
else
{
echo "URL Invalid";
}
This regex will validate nearly all valid url’s and is handy to have knocking about.

Thanks to the original author, whoever that may be…..