$re = '/(?s).*?(\z|\d+\.\d+\.\d+\.\d+)/m';
$str = 'Nmap scan report for 192.168.0.21
Host is up (0.18s latency).
Not shown: 1 filtered port
Some closed ports may be reported as filtered due to --defeat-rst-ratelimit
PORT STATE SERVICE
22/tcp open ssh
Nmap scan report for 192.168.0.29
Host is up (0.029s latency).
Not shown: 1 filtered port
Some closed ports may be reported as filtered due to --defeat-rst-ratelimit
PORT STATE SERVICE
22/tcp open ssh
Nmap scan report for 192.168.0.25
Host is up (0.15s latency).
Not shown: 1 filtered port
Some closed ports may be reported as filtered due to --defeat-rst-ratelimit
PORT STATE SERVICE
22/tcp open ssh';
$subst = "$1\n";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php