# Expression régulière¶

The following description is an overview of available signs which can be used in regular expressions. This chapter is supposed to be a references for the different regex elements.

## Common matching symbols¶

Regular Expression Description
.
Matches any character
^regex
regex must match at the beginning of the line
regex$ Finds regex must match at the end of the line [abc]  Set definition, can match the letter a or b or c [abc][vz] Set definition, can match a or b or c followed by either v or z [^abc] When a "^" appears as the first character inside [] when it negates the pattern. This can match any character except a or b or c [a-d1-7] Ranges, letter between a and d and figures from 1 to 7, will not match d1 X|Z  Finds X or Z XZ  Finds X directly followed by Z $
Checks if a line end follows

## Metacharacters¶

The following metacharacters have a pre-defined meaning and make certain common pattern easier to use, e.g. \d instead of [0..9].

Regular Expression Description
\d
Any digit, short for [0-9]
\D
A non-digit, short for [^0-9]
\s
A whitespace character, short for [ \t\n\x0b\r\f]
\S
A non-whitespace character, for short for [^\s]
\w
A word character, short for [a-zA-Z_0-9]
\W
A non-word character [^\w]
\S+
Several non-whitespace characters
\b
Matches a word boundary. A word character is [a-zA-Z0-9_] and \b matches its bounderies.

## Quantifier¶

A quantifier defines how often an element can occur. The symbols ?, *, + and {} define the quantity of the regular expressions

Regular Expression Description
*
Occurs zero or more times, is short for {0,}
+
Occurs one or more times, is short for {1,}
?
Occurs no or one times, ? is short for {0,1}
{X}
Occurs X number of times, {} describes the order of the preceding liberal
{X,Y}
Occurs between X and Y times
*?
? after a qualifier makes it a "reluctant quantifier", it tries to find the smallest match.