# Yapbam : Help

## Regular expressions

A regular expression is a pattern that describes the set of all possibles characters string.It has a very precise and complex syntax that you could find below in the Sun documentation (in the external links section).

### Here are some parts of the syntax :

- Quantifiers:
  - *: X* means 0 or more instance of X.
  - ?: X? means 0 or 1 instance of X.
  - +: X+ means 1 or more instance of X.
- Position:
  - ^: The beginning of the string.
  - $: The end of the string.
- Character class:
  - .: Any character.
  - \d: A digit character [0-9].

### Here are some examples that could be helpful :

- start.* : all strings that begin with "start".
- .*end$ : all strings that end with "end".
- .*\d+ : all strings that contains some digits.

## External links

- Sun documentation about Java regular expressions
- Wikipedia page about regular expressions