$re = '/(?<=:\s).*/m';
$str = 'Turning on API signature validation for service : PGL
Turning off API signature validation for service : PLATFORM
Turning off API signature validation for service : WEBWORKS
Turning on API signature validation for service : TIMER_SINK
Turning on API signature validation for service : MESSAGING
Turning on API signature validation for service : EMAIL
Turning off API signature validation for service : USER_SECURITY
Initializing MDM for :USER_SECURITY
<MDM/>';
$subst = "$1";
$result = preg_replace($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