regular expressions for pattern

October 21, 2017

Common Matching Expressions

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

Regular Expression

Description

.

Matches any character

^regex

Finds regex that must match at the beginning of the line.

regex$

Finds regex that 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 caret appears as the first character inside square brackets, it negates the pattern. This pattern matches any character except a or b or c.

[a-d1-7]

Ranges: matches a letter between a and d and figures from 1 to 7, but not 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 patterns 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, short for

`\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 where a word character is `[a-zA-Z0-9_]`

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, short for
`\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 where a word character is `[a-zA-Z0-9_]`

Quantifier

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

Regular Expression Description Examples

Regular Expression	Description	Examples
`*`	Occurs zero or more times, is short for `{0,}`	`X` finds no or several letter X, <sbr /> `.` finds any character sequence
`+`	Occurs one or more times, is short for `{1,}`	`X+`- Finds One or several letters X
`?`	Occurs no or one time, `?` is short for `{0,1}`.	`X?` finds no or exactly one letter X
`{X}`	Occurs X number of times, `{}`describes the order of the preceding liberal	`\d{3}` searches for three digits, `.{10}` for any character sequence of length 10.
`{X,Y}`	Occurs between X and Y times,	`\d{1,4}` means `\d` must occur at least once and at a maximum of four.
`*?`	`?` after a quantifier makes it a reluctant quantifier. It tries to find the smallest match. This makes the regular expression stop at the first match.

*

Occurs zero or more times, is short for {0,}

X* finds no or several letter X, <sbr /> .* finds any character sequence

+

Occurs one or more times, is short for {1,}

X+- Finds One or several letters X

?

Occurs no or one time, ? is short for {0,1}.

X? finds no or exactly one letter X

{X}

Occurs X number of times, {}describes the order of the preceding liberal

\d{3} searches for three digits, .{10} for any character sequence of length 10.

{X,Y}

Occurs between X and Y times,

\d{1,4} means \d must occur at least once and at a maximum of four.

*?

? after a quantifier makes it a reluctant quantifier. It tries to find the smallest match. This makes the regular expression stop at the first match.