Regular Expressions

The following tables provide a overview of the regular expressions syntax. See also Python regular expressions description in the Python re module.

Special Characters

Description

.

Matches any character (dot).

^

“^…”, matches start-of-string (caret).

$

“…$”, matches end-of-string (dollar sign).

|

“A|B”, matches “A” or “B”.

\

Escape character.

\.

EXAMPLE: Matches character ‘.’ (dot).

\\

EXAMPLE: Matches character ‘\’ (backslash).

To select or match characters from a special set of characters, a character set must be defined.

Character sets

Description

[...]

Define a character set, like [A-Za-z].

\d

Matches digit character: [0-9]

\D

Matches non-digit character.

\s

Matches whitespace character: [ \t\n\r\f\v]

\S

Matches non-whitespace character

\w

Matches alphanumeric character: [a-zA-Z0-9_]

\W

Matches non-alphanumeric character.

A text part must be group to extract it as part (parameter).

Grouping

Description

(...)

Group a regular expression pattern (anonymous group).

\number

Matches text of earlier group by index, like: “\1”.

(?P<name>...)

Matches pattern and stores it in parameter “name”.

(?P=name)

Match whatever text was matched by earlier group “name”.

(?:...)

Matches pattern, but does non capture any text.

(?#...)

Comment (is ignored), describes pattern details.

If a group, character or character set should be repeated several times, it is necessary to specify the cardinality of the regular expression pattern.

Cardinality

Description

?

Pattern with cardinality 0..1: optional part (question mark).

*

Pattern with cardinality zero or more, 0.. (asterisk).

+

Pattern with cardinality one or more, 1.. (plus sign).

{m}

Matches m repetitions of a pattern.

{m,n}

Matches from m to n repetitions of a pattern.

[A-Za-z]+

EXAMPLE: Matches one or more alphabetical characters.