Check if given domain list have same ip (living in the same server instance)

is_same_server.php

#!/usr/bin/env php
<?php

if ($argc < 3) {
    echo sprintf('%s <domainList> <domain/ip>%s', $argv[0], PHP_EOL);
    exit(1);
}

/**
 * ValidateDomainOrIp
 *
 * @param string $domainOrIp
 * @return array|false
 */
function validateDomainOrIp($domainOrIp): array|false  // Returns array of IP addresses or false if invalid input
{
    $ips = [];

    if (filter_var($domainOrIp, FILTER_VALIDATE_IP)) {
        $ips[] = $domainOrIp;
    } else if (filter_var($domainOrIp, FILTER_VALIDATE_DOMAIN)) {
        $ips = gethostbynamel($domainOrIp);
    }
    return $ips;
}

if (($inputIps = validateDomainOrIp($argv[2])) == false) {
    echo sprintf('%s Is invalid or dead domain%s', $argv[2], PHP_EOL);
    exit(1);
}

$domainList = file($argv[1], FILE_SKIP_EMPTY_LINES | FILE_IGNORE_NEW_LINES);
$hosts = [];

foreach ($domainList as $domain) {
    if (($ips = gethostbynamel($domain)) == false) {
        continue;
    }
    foreach ($inputIps as $inputIp) {
        if (in_array($inputIp, $ips)) {
            $hosts[$domain][] = $inputIp; // for later use
            echo $domain, PHP_EOL; // output domain that has the same ip
        }
    }
}

//print_r($hosts);