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

using php, how validate string valid ip?

examples of valid strings:

• 192.158.5.95
• 121.212
• 12.12.12.204

examples of invalid strings:

• 121
• 10 12 12 (no dots)

my current script uses code, insufficient needs:

if(strpos($input, '.') !== false) {       // there period  }  else  {        // no period  }  

as such, can please advise how can validate string valid ip?

$valid = ip2long($ip) !== false;