It’s always good to have the most used htaccess regular expressions in one place. Here is a little help (cheat-sheet), which contains all the special characters which you can use in your htaccess file to rewrite the urls:

. (full stop) – match any character
* (asterix) – match zero or more of the previous symbol
+ (plus) – match one or more of the previous symbol
? (question) – match zero or one of the previous symbol
\? (backslash-something) – match special characters
^ (caret) – match the start of a string
$ (dollar) - match the end of a string
[set] – match any one of the symbols inside the square braces.
(pattern) – grouping, remember what the pattern matched as a special variable