How can I simply validate whether a string is a valid IP in PHP?

Question

Using PHP, how do I validate that a string is a valid IP?

Examples of valid strings:

• 192.158.5.95
• 121.212
• 12.12.12.204

Answer 1

Just in case there's anyone that doesn't want to use the ip2long function, here is a simple function (Idea taken from a class in osTicket):

function is_ip( $ip = null ) {

    if( !$ip or strlen(trim($ip)) == 0){
        return false;
    }

    $ip=trim($ip);
    if(preg_match("/^[0-9]{1,3}(.[0-9]{1,3}){3}$/",$ip)) {
        foreach(explode(".", $ip) as $block)
            if($block<0 || $block>255 )
                return false;
        return true;
    }
    return false;
}