Simple PHP snippet to validate a URL using preg_match

Validate URL

<?php

function isValidURL($url){
return preg_match('|^http(s)?://[a-z0-9-]+(.[a-z0-9-]+)*(:[0-9]+)?(/.*)?$|i', $url);
}

// usage
if(!isValidURL($url)){
$message = 'Please enter a valid URL';
echo $message;
}

By not deeply checking the returned value then you are evaluating 0 and null as the same, from the documentation:

Return Values

preg_match() returns 1 if the pattern matches given subject, 0 if it does not, or false if an error occurred.
Warning

This function may return Boolean false, but may also return a non-Boolean value which evaluates to false. Please read the section on Booleans for more information. Use the === operator for testing the return value of this function.