Regex: List of Metacharacters

List of meta characters used in regular expressions. Positioning, Special characters, Lazy, Greedy, Lookahead, Lookbehind, etc.

Positional / Special characters

Positional

Metacharacter	Description
`^`	Beginning of line
`$`	End of line
`\A`	Beginning of string
`\z`	End of string
`\Z`	End of string (excluding line endings)
`\b`	Word boundaries
`\B`	Non-word boundaries

* The ^ and $ are used as "beginning and end of line" but this is the case in multiline mode (usually this is the default). In single-line mode, it is the beginning or end of the entire string.

Special characters

Metacharacter	Description
`\`	Escape
`\t`	Tab
`\n`	Newline (CR)
`\r`	Newline (LF)
`\f`	New page
`\d`	Digits
`\D`	Non-digits
`\s`	Whitespace (space, tab, neewline and new page)
`\S`	Non-whitespace
`\w`	Word (alphanumeric characters plus "_")
`\W`	Non-word

Wildcards and repetition (quantity specifiers)

Default	Lazy	Greedy	Description
`.`			Any one character (excluding line feed code)
`*`	`*?`	`*+`	1 character/group immediately preceding 0 or more times
`+`	`+?`	`++`	1 character/group immediately preceding 1 or more times
`?`	`??`	`?+`	1 character/group immediately preceding 0 or 1 times
`{n}`	`{n}?`	`{n}+`	1 character/group immediately preceding n times
`{n,}`	`{n,}?`	`{n,}+`	1 character/group immediately preceding n or more times
`{n,m}`	`{n,m}?`	`{n,m}+`	1 character/group immediately preceding n or more times, but not more than m times.

Default

Match the longest part that matches the condition. Preference is given to matching the entire pattern.

Lazy

Match the shortest part that matches the condition.

Greedy

Match the longest part that matches the condition. No preference is given to matching the entire pattern.

e.g. abcXdefX

	Regex	Result
Default	`^.*X`	`abcXdefX`
Lazy	`^.*?X`	`abcX`
Greedy	`^.*+X`	Not match.^*
Greedy	`^.*+`	`abcXdefX`

(*) "^.*+" matches all "abcXdefX", so the last `X` does not match.

Positional

Metacharacter	Description
`()`	Blocking
`\|`	Or (strings)
`[]`	Or (one character)

e.g. |

Regex	Description
`abc\|mno\|xyz`	Simple abc, mno, or xyz
`abc.*X\|m+o\|xy?z`	Include metachar in candidates abcXXX, mXo, xz, etc.
`(abc\|mno\|xyz)X`	Combine with other strings abcX, mnoX, or xyzX
`(abc\|mno\|xyz)*`	Combine with quantity specifiers abcabc, mnoabcxyz, etc.

e.g. []

Regex	Description
`[abc]`	Simple (a, b, or c)
`[^abc]`	Negation (Other than a, b, c)
`[a-z]`	Range (lowercase)
`[A-Z]`	Range (uppercase)
`[0-9]`	Range (digits)
`[a-zA-Z]`	Or (a to z or A to Z)
`[a-z&&[d-f]]`	And (a to z and d to f)
`[a-z&&[^d-f]]`	Subtraction (a to z excluding d to f)

Lookahead and Lookbehind

Metacharacter	Description	e.g.	Description
`?=`	Positive lookahead	`foo(?=bar)`	Matches "foo" followed by "bar".
`?!`	Negative lookahead	`foo(?!bar)`	Matches "foo" not followed by "bar".
`?<=`	Positive lookbehind	`(?<=bar)foo`	Matches "foo" preceded by "bar".
`?<!`	Negative lookbehind	`(?<!bar)foo`	Matches "foo" not preceded by "bar".

2018-02-03