check if a string is a URL [duplicate]

Answer 1

Something like might work for you:

$arr = array('abc.com/foo',
'localhost',
'abc+def',
'how r u',
'https://how r u',
'ftp://abc.com',
'a.b');
foreach ($arr as $u) {
   $url = $u;
   if (!preg_match('#^(?:https?|ftp)://#', $url, $m))
      $url = 'http://' . $url;
   echo "$u => ";
   var_dump(filter_var($url, FILTER_VALIDATE_URL));
}

OUTPUT:

abc.com/foo => string(18) "http://abc.com/foo"
localhost => string(16) "http://localhost"
abc+def => string(14) "http://abc+def"
how r u => bool(false)
https://how r u => bool(false)
ftp://abc.com => string(13) "ftp://abc.com"
a.b => string(10) "http://a.b"

So basically wherever you notice false as return value that is an INVALID URL for you.

Answer 2

http://www.php.net/manual/en/function.preg-match.php#93824

<?php 
    $regex = "((https?|ftp)\:\/\/)?"; // SCHEME 
    $regex .= "([a-z0-9+!*(),;?&=\$_.-]+(\:[a-z0-9+!*(),;?&=\$_.-]+)?@)?"; // User and Pass 
    $regex .= "([a-z0-9-.]*)\.([a-z]{2,3})"; // Host or IP 
    $regex .= "(\:[0-9]{2,5})?"; // Port 
    $regex .= "(\/([a-z0-9+\$_-]\.?)+)*\/?"; // Path 
    $regex .= "(\?[a-z+&\$_.-][a-z0-9;:@&%=+\/\$_.-]*)?"; // GET Query 
    $regex .= "(#[a-z_.-][a-z0-9+\$_.-]*)?"; // Anchor 

       if(preg_match("/^$regex$/i", $url)) // `i` flag for case-insensitive
       { 
               return true; 
       } 
?>

but your example URL is over simplified, (\w+)\.(\w+) would match it. somebody else mentioned filter_var which is simply a filter_var($url, FILTER_VALIDATE_URL) but it doesn't seem to like non-ascii characters so, beware...