Regular expressions are a central concept in computer sciences. They denote expressions that can be translated into a finite set of character strings (i.e. sequences). They allow ambiguities (e.g. a or b), wild cards (any character) etc. In sequence analysis we use regular expression definitions closely related to that found in the UNIX system. Typical examples of operators:

Example

Meaning

[AF]

A or F

x

any character

-

gap

.

any character or gap

A{5,10}

minimum 5, maximum 10 A's