Domain Info script - attempts to give you registrar nameservers, basic DNS, actual hostname hosting the domain and MX records

domain_info.php

<?php
/*
 * This needs comments and command-line arguments and stuff. It's ruff and ready.
 */

global $domain_re;

$domain_re = '([0-9a-zA-Z\-]+\.)+[0-9a-zA-Z\-]+';

function get_nameservers( $whois_out, $domain ) {
	if ('.uk' == substr($domain, -3)) {
		return get_uk_nameservers( $whois_out );
	} else {
		return get_nonuk_nameservers( $whois_out );
	}
}

function get_registrar( $whois_out, $domain ) {
	if ('.uk' == substr($domain, -3)) {
		return get_uk_registrar( $whois_out );
	} else {
		return get_nonuk_registrar( $whois_out );
	}
}

function get_uk_registrar( $whois_out ) {
	
	global $domain_re;

	$found_intro = false;
	$no_more = false;
	$registrar_lines = [];
	
	foreach ( $whois_out as $line ) {
		if (! $no_more) {
			if ( $found_intro ) {
				if (!empty($line)) {
					$registrar_lines[] = trim($line);
				} else {
					$no_more = true;
				}
			}
			else if ( false !== strpos( $line, "Registrar:" ) ) {
				$found_intro = true;
			}
		}
	}
	
	return $registrar_lines;

}

function get_nonuk_registrar( $whois_out ) {
	
	global $domain_re;

	$registrar_lines = [];
	
	foreach( $whois_out as $line ) {
		if (preg_match( '/Sponsoring Registrar:\s+(.*)$/', $line, $matches ) ) {
			$registrar_lines[] = $matches[1];
		}
	}
	return $registrar_lines;
}


function get_uk_nameservers( $whois_out ) {
	
	global $domain_re;

	$found_intro = false;
	$no_more = false;
	$servers = [];
	
	foreach ( $whois_out as $line ) {
		if (! $no_more) {
			if ( $found_intro ) {
				if (preg_match( '/(' . $domain_re . ')/', $line, $matches ) ) {
					$servers[] = $matches[0];
				} else {
					$no_more = true;
				}
			}
			else if ( false !== strpos( $line, "Name servers:" ) ) {
				$found_intro = true;
			}
		}
	}
	
	return $servers;

}

function get_nonuk_nameservers( $whois_out ) {
	
	global $domain_re;

	$servers = [];
	
	foreach( $whois_out as $line ) {
		if (preg_match( '/Name Server:\s+(' . $domain_re . ')/', $line, $matches ) ) {
			$servers[] = $matches[1];
		}
	}
	return $servers;
}

function get_mxs( $mx_out ) {
	
	global $domain_re;

	$mxs = [];
	
	foreach( $mx_out as $line ) {
		if (preg_match( '/IN\s+MX\s+(\d+\s+' . $domain_re . ')/', $line, $matches ) ) {
			$mxs[] = $matches[1];
		}
	}
	return $mxs;
}


function get_hostname( $host_out ) {

	global $domain_re;

	$hostname = 'unknown';
	
	foreach( $host_out as $line ) {
		if (preg_match( '/PTR\s+(' . $domain_re . ')/', $line, $matches ) ) {
			$hostname = $matches[1];
		}
	}

	return $hostname;
}

function output_registrar( $registrar_lines ) {
	echo "\nRegistrar: \n";
	echo "  " . implode("\n  ", $registrar_lines);
	echo "\n\n";
}

function output_nameservers( $nameservers ) {
	echo "Nameservers: \n";
	echo "  " . implode("\n  ", $nameservers);
	echo "\n\n";
}

function output_dns( $dns ) {
	echo "DNS lookup: \n";
	echo "  $dns\n\n";
}

function output_hostname( $hostname, $dns ) {
	echo "Hostname (of $dns): \n";
	echo "  $hostname\n\n";
}

function output_mxs( $mxs ) {
	echo "MX records: \n";
	echo "  " . implode("\n  ", $mxs);
	echo "\n\n";
}

$domain = $argv[1];

$whois = exec('whois ' . $domain, $whois_out);
$dns = exec('dig +short ' . $domain);
$host = exec('dig -x ' . $dns, $host_out);
$mx = exec('dig ' . $domain . ' mx', $mx_out);

$registrar_lines = get_registrar($whois_out, $domain);
$nameservers = get_nameservers($whois_out, $domain);
$hostname = get_hostname( $host_out );
$mxs = get_mxs( $mx_out );

output_registrar( $registrar_lines );
output_nameservers( $nameservers );
output_dns( $dns );
output_hostname( $hostname, $dns );
output_mxs( $mxs );