Useful Regex
Searching for a text preceded by a question mark (?)
(?<=\?)(.*)
Input: derpderp?mystring blahbeh
Output: mystring blahbeh
Positive lookahead technique
(.+)(?=&)
Take anything until the last "&"
(.+?)(?=&)
Take anything until the first "&"
Mix both techniques and you can select a part of aa string between two characters.
(?<=\?)(.+)(?=blah)
In this example:
Input:Derpderp?mystringblahbeh
Output: mystring