$re = '/@shader\(([^)]*)\):(?:\r?\n)((?:[^@]|@(?!shader))*)/';
$str = '@shader(vertex):
...shader data...
@shader(fragment):
...shader data...';
$subst = " $0";
$result = preg_replace($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