$re = '/^(.*?ChangePack-[a-zA-Z0-9]+)/m';
$str = '/Repository/Framework/PITA/branches/ChangePack-6a7B6/core/src/Pita.x86.Interfaces/IDemoReader.cs
/Repository/Demo1/Demo2/4.3//PITA/branches/ChangePack-6a7B6/core/src/Pita.x86.Interfaces
/Repository/Framework/ChangePack-7/branches/ChangePack-6a7B6/hh1';
preg_match_all($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