You should not be permitted to write production code if you do not have an journeyman licence in regular expressions or floating point math. —Rob Pike
#+begin_src sh . single character \ escape ? optional character
zero or more of previous
- one ore more
| or on the word level |
[] or for specific characters ^ not \d digit \s whitespace (tabs, carriage returns, null) \b word boundary \d{4} equiv \d\d\d\d parenthesis and ? makes the stuff in parens optional same for + and * \w{n} n letter words \w{n,k} n or k letter words #+end_src