$re = '/(?:core|proxy|error|get):(.+?)(?=(core|proxy|error|get):|$)/i';
$str = 'Core:init Proxy: Attemps is ended. Error: Proxy connect timeout Error: core unknown Core:error parse line';
preg_match_all($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