$re = '/<value>[\s\S]*?(([0-2]?[0-9]?[0-9]\.){3}([0-2]?[0-9]?[0-9]))[\s\S]*?<\/value>/';
$str = '<value>activemq:tcp://192.168.0.172:61616?transport.useInactivityMonitor=false</value>
<value>192.168.0.172</value>';
$subst = "{$1 $2 $3}";
$result = preg_replace($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