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

If @Tomgrohl brought up regexes, you can do it in one line:

function is_ip($ip) {
    return is_string($ip) && preg_match('/^([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-5][0-5])\.([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-5][0-5])\.([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-5][0-5])\.([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-5][0-5])$/');
}

Explanation:

/ // regex delimiter
    ( // start grouping
        [0-9] // matches from 0 to 9
        | // or
        [1-9][0-9] // matches from 10 to 99
        | // or
        1[0-9]{2} // matches from 100 to 199
        | // or
        2[0-5][0-5] // matches from 200 to 255
    ) stop grouping
    \. // matches the dot
    // the rest (same) of the numbers
/ regex delimiter

Online tester: https://regex101.com/r/eM4wB9/1
Note: it only matches ipv4