\a

Matches a bell character, \u0007.

\a

"\u0007" in "Error!" + '\u0007'

\b

In a character class, matches a backspace, \u0008.

[\b]{3,}

"\b\b\b\b" in "\b\b\b\b"

\t

Matches a tab, \u0009.

(\w+)\t

"item1\t", "item2\t" in "item1\titem2\t"

\r

Matches a carriage return, \u000D. (\r is not equivalent to the newline character, \n.)

\r\n(\w+)

"\r\nThese" in "\r\nThese are\ntwo lines."

\v

Matches a vertical tab, \u000B.

[\v]{2,}

"\v\v\v" in "\v\v\v"

\f

Matches a form feed, \u000C.

[\f]{2,}

"\f\f\f" in "\f\f\f"

\n

Matches a new line, \u000A.

\r\n(\w+)

"\r\nThese" in "\r\nThese are\ntwo lines."

\e

Matches an escape, \u001B.

\e

"\x001B" in "\x001B"

\octal

Uses octal representation to specify a character (octal consists of up to three digits).

\w\040\w

"a b", "c d" in

"a bc d"

\xhex

Uses hexadecimal representation to specify a character (hex consists of exactly two digits).

\w\x20\w

"a b", "c d" in

"a bc d"

\cchar

Matches the ASCII control character that is specified by char.

\cC

"\x0003" in "\x0003" (Ctrl-C)

\u0020

Matches a Unicode character by using hexadecimal representation (exactly four digits).

\w\u0020\w

"a b", "c d" in

"a bc d"

\

When followed by a character that is not recognized as an escaped character in this and other tables in this topic, matches that character. For example, \* is the same as \x2A. This allows the regular expression engine to disambiguate language elements (such as * or ?) and character literals (represented by \* or \?).

\d+[\+-x\*]\d+\d+[\+-x\*\d+

"2+2" and "3*9" in "(2+2) * 3*9"

[character_group]

Matches any single character in character_group. By default, the match is case-sensitive.

[ae]

"a" in "gray"

"a", "e" in "lane"

[^character_group]

Negation: Matches any single character that is not in character_group. By default, characters in character_group are case-sensitive.

[^aei]

"r", "g", "n" in "reign"

[first-last]

Character range: Matches any single character in the range from first to last.

[A-Z]

"A", "B" in "AB123"

.

Wildcard: Matches any single character except \n.

a.e

"ave" in "nave"

"ate" in "water"

\p{name}

Matches any single character in the Unicode general category or named block specified by name.

\p{Lu}

\p{IsCyrillic}

"C", "L" in "City Lights"

"Д", "Ж" in "ДЖem"

\P{name}

Matches any single character that is not in the Unicode general category or named block specified by name.

\P{Lu}

\P{IsCyrillic}

"i", "t", "y" in "City"

"e", "m" in "ДЖem"

\w

Matches any word character.

\w

"I", "D", "A", "1", "3" in "ID A1.3"

\W

Matches any non-word character.

\W

" ". "." in "ID A1.3"

\s

Matches any white-space character.

\w\s

"D " in "ID A1.3"

\S

Matches any non-white-space character.

\s\S

" _" in "int __ctr"

\d

Matches any decimal digit.

\d

"4" in "4 = IV"

\D

Matches any non-decimal digit.

\D

" ", "=", " ", "I", "V" in "4 = IV"

^

The match must start at the beginning of the string or line.

^\d{3}

"901-" in

"901-333-"

$

The match must occur at the end of the string or before \n at the end of the line or string.

-\d{3}$

"-333" in

"-901-333"

\A

The match must occur at the start of the string.

\A\d{3}

"901-" in

"901-333-"

\Z

The match must occur at the end of the string or before \n at the end of the string.

-\d{3}\Z

"-333" in

"-901-333"

\z

The match must occur at the end of the string.

-\d{3}\z

"-333" in

"-901-333"

\G

The match must occur at the point where the previous match ended.

\G\(\d\)

"(1)", "(3)", "(5(" in "(1)(3)(5)[7](9)"

\b

The match must occur on a boundary between a \w (alphanumeric) and a \W (nonalphanumeric) character.

\b\w+\s\w+\b

"them them" in "them theme them them"

\B

The match must not occur on a \b boundary.

\Bend\w*\b

"ends", "ender" in "end sends endure lender"

(subexpression)

Captures the matched subexpression and assigns it a zero-based ordinal number.

(\w)\1

"ee" in "deep"

(?<name> subexpression)

Captures the matched subexpression into a named group.

(?<double>\w)\k<double>

"ee" in "deep"

(?<name1-name2> subexpression)

Defines a balancing group definition.

(((?'Open'\()[^\(\)]*)+((?'Close-Open'\))[^\(\)]*)+)*(?(Open)(?!))$

"((1-3)*(3-1))" in "3+2^((1-3)*(3-1))"

(?: subexpression)

Defines a noncapturing group.

Write(?:Line)?

"WriteLine" in "Console.WriteLine()"

(?imnsx-imnsx: subexpression)

Applies or disables the specified options within subexpression. For more information, see Regular Expression Options.

A\d{2}(?i:\w+)\b

"A12xl", "A12XL" in "A12xl A12XL a12xl"

(?= subexpression)

Zero-width positive lookahead assertion.

\w+(?=\.)

"is", "ran", and "out" in "He is. The dog ran. The sun is out."

(?! subexpression)

Zero-width negative lookahead assertion.

\b(?!un)\w+\b

"sure", "used" in "unsure sure unity used"

(?<= subexpression)

Zero-width positive lookbehind assertion.

(?<=19)\d{2}\b

"99", "50", "05" in "1851 1999 1950 1905 2003"

(?<! subexpression)

Zero-width negative lookbehind assertion.

(?<!19)\d{2}\b

"51", "03" in "1851 1999 1950 1905 2003"

(?> subexpression)

Nonbacktracking (or "greedy") subexpression.

[13579](?>A+B+)

"1ABB", "3ABB", and "5AB" in "1ABB 3ABBC 5AB 5AC"

*

Matches the previous element zero or more times.

\d*.\d

".0", "19.9", "219.9"

+

Matches the previous element one or more times.

"be+"

"bee" in "been", "be" in "bent"

?

Matches the previous element zero or one time.

"rai?n"

"ran", "rain"

{n}

Matches the previous element exactly n times.

",\d{3}"

",043" in "1,043.6", ",876", ",543", and ",210" in "9,876,543,210"

{n,}

Matches the previous element at least n times.

"\d{2,}"

"166", "29", "1930"

{n,m}

Matches the previous element at least n times, but no more than m times.

"\d{3,5}"

"166", "17668", "19302" in "193024"

*?

Matches the previous element zero or more times, but as few times as possible.

\d*?.\d

".0", "19.9", "219.9"

+?

Matches the previous element one or more times, but as few times as possible.

"be+?"

"bee" in "been", "be" in "bent"

??

Matches the previous element zero or one time, but as few times as possible.

"rai??n"

"ran", "rain"

{n}?

Matches the preceding element exactly n times.

",\d{3}?"

",043" in "1,043.6", ",876", ",543", and ",210" in "9,876,543,210"

{n,}?

Matches the previous element at least n times, but as few times as possible.

"\d{2,}?"

"166", "29", "1930"

{n,m}?

Matches the previous element between n and m times, but as few times as possible.

"\d{3,5}?"

"166", "17668", "19302" in "193024"

\number

Backreference. Matches the value of a numbered subexpression.

(\w)\1

"ee" in "seek"

\k<name>

Named backreference. Matches the value of a named expression.

(?<char>\w)\k<char>

"ee" in "seek"

|

Matches any one element separated by the vertical bar (|) character.

th(e|is|at)

"the", "this" in "this is the day. "

(?(expression)yes|no)

Matches yes if expression matches; otherwise, matches the optional no part. expression is interpreted as a zero-width assertion.

(?(A)A\d{2}\b|\b\d{3}\b)

"A10", "910" in "A10 C103 910"

(?(name)yes|no)

Matches yes if the named capture name has a match; otherwise, matches the optional no.

(?<quoted>")?(?(quoted).+?"|\S+\s)

Dogs.jpg, "Yiska playing.jpg" in "Dogs.jpg "Yiska playing.jpg""

$number

Substitutes the substring matched by group number.

/b(/w+)(/s)(/w+)/b

$3$2$1

"one two"

"two one"

${name}

Substitutes the substring matched by the named group name.

\b(?<word1>\w+)(\s)(?<word2>\w+)\b

${word2} ${word1}

"one two"

"two one"

$$

Substitutes a literal "$".

\b(\d+)\s?USD

$$$1

"103 USD"

"$103"

$&

Substitutes a copy of the whole match.

(\$*(\d*(\.+\d+)?){1})

**$&

"$1.30"

"**$1.30**"

$`

Substitutes all the text of the input string before the match.

B+

$`

"AABBCC"

"AAAACC"

$'

Substitutes all the text of the input string after the match.

B+

$'

"AABBCC"

"AACCCC"

$+

Substitutes the last group that was captured.

B+(C+)

$+

"AABBCCDD"

AACCDD

$_

Substitutes the entire input string.

B+

$_

"AABBCC"

"AAAABBCCCC"

(?imnsx-imnsx)

Sets or disables options such as case insensitivity in the middle of a pattern. For more information, see Regular Expression Options.

\bA(?i)b\w+\b matches "ABA", "Able" in "ABA Able Act"

(?# comment)

Inline comment. The comment ends at the first closing parenthesis.

\bA(?#Matches words starting with A)\w+\b

# [to end of line]

X-mode comment. The comment starts at an unescaped # and continues to the end of the line.

(?x)\bA\w+\b#Matches words starting with A

August 2009

Revised extensively.

Information enhancement.