> uploadtext_

<?php

function isValidIPv4(string $ip): bool {
    // Regex for IPv4 validation.
    // It checks for four octets (0-255) separated by dots.
    // Anchors ^ and $ ensure the entire string matches the pattern.
    $ipv4_regex = '/^((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$/';
    return (bool) preg_match($ipv4_regex, $ip);
}

$ip1 = "192.168.1.1";
$ip2 = "255.255.255.0";
$ip3 = "10.0.0.256"; // Invalid
$ip4 = "abc.def.ghi.jkl"; // Invalid
$ip5 = "172.16.0.1";

echo "$ip1 is valid: " . (isValidIPv4($ip1) ? "Yes" : "No") . "
";
echo "$ip2 is valid: " . (isValidIPv4($ip2) ? "Yes" : "No") . "
";
echo "$ip3 is valid: " . (isValidIPv4($ip3) ? "Yes" : "No") . "
";
echo "$ip4 is valid: " . (isValidIPv4($ip4) ? "Yes" : "No") . "
";
echo "$ip5 is valid: " . (isValidIPv4($ip5) ? "Yes" : "No") . "
";

?>