$re = '/(?ms).*message=(?<Msg>.+)/m';
$str = 'ERROR | 2023-03-16 01:27:14 EDT | field1=field1_value | field2=field2_value | field3=field3_value | field4=field4_value | field5=field5_value | field6=field6_value | field7={} | message=Message String with spaces.
java.stacktrace.Exception: Exception Details.
at ...
at ...
at ...
at ...';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
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