正则表达式语法规则收集

Escaped character

Description

ordinary characters

Characters other than . $ ^ { [ ( | ) * + ? / match themselves.

/a

Matches a bell (alarm) /u0007.

/b

Matches a backspace /u0008 if in a [] character class; otherwise, see the note following this table.

/t

Matches a tab /u0009.

/r

Matches a carriage return /u000D.

/v

Matches a vertical tab /u000B.

/f

Matches a form feed /u000C.

/n

Matches a new line /u000A.

/e

Matches an escape /u001B.

/040

Matches an ASCII character as octal (up to three digits); numbers with no leading zero are backreferences if they have only one digit or if they correspond to a capturing group number. (For more information, see Backreferences.) For example, the character /040 represents a space.

/x20

Matches an ASCII character using hexadecimal representation (exactly two digits).

/cC

Match+es an ASCII control character; for example, /cC is control-C.

/u0020

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

/

When followed by a character that is not recognized as an escaped character, matches that character. For example, /* is the same as /x2A.

Character class

Description

.

Matches any character except /n. If modified by the Singleline option, a period character matches any character. For more information, see Regular Expression Options.

[aeiou]

Matches any single character included in the specified set of characters.

[^aeiou]

Matches any single character not in the specified set of characters.

[0-9a-fA-F]

Use of a hyphen (–) allows specification of contiguous character ranges.

/p{name}

Matches any character in the named character class specified by {name}. Supported names are Unicode groups and block ranges. For example, Ll, Nd, Z, IsGreek, IsBoxDrawing.

/P{name}

Matches text not included in groups and block ranges specified in {name}.

/w

Matches any word character. Equivalent to the Unicode character categories
[/p{Ll}/p{Lu}/p{Lt}/p{Lo}/p{Nd}/p{Pc}]. If ECMAScript-compliant behavior is specified with the ECMAScript option, /w is equivalent to [a-zA-Z_0-9].

/W

Matches any nonword character. Equivalent to the Unicode categories [^/p{Ll}/p{Lu}/p{Lt}/p{Lo}/p{Nd}/p{Pc}]. If ECMAScript-compliant behavior is specified with the ECMAScript option, /W is equivalent to [^a-zA-Z_0-9].

/s

Matches any white-space character. Equivalent to the Unicode character categories [/f/n/r/t/v/x85/p{Z}]. If ECMAScript-compliant behavior is specified with the ECMAScript option, /s is equivalent to [ /f/n/r/t/v].

/S

Matches any non-white-space character. Equivalent to the Unicode character categories [^/f/n/r/t/v/x85/p{Z}]. If ECMAScript-compliant behavior is specified with the ECMAScript option, /S is equivalent to [^ /f/n/r/t/v].

/d

Matches any decimal digit. Equivalent to /p{Nd} for Unicode and [0-9] for non-Unicode, ECMAScript behavior.

/D

Matches any nondigit. Equivalent to /P{Nd} for Unicode and [^0-9] for non-Unicode, ECMAScript behavior.

RegexOption member

Inline character

Description

None

N/A

Specifies that no options are set.

IgnoreCase

i

Specifies case-insensitive matching.

Multiline

m

Specifies multiline mode. Changes the meaning of ^ and $ so that they match at the beginning and end, respectively, of any line, not just the beginning and end of the whole string.

ExplicitCapture

n

Specifies that the only valid captures are explicitly named or numbered groups of the form (?<name>…). This allows parentheses to act as noncapturing groups without the syntactic clumsiness of (?:…).

Compiled

N/A

Specifies that the regular expression will be compiled to an assembly. Generates Microsoft intermediate language (MSIL) code for the regular expression; yields faster execution at the expense of startup time.

Singleline

s

Specifies single-line mode. Changes the meaning of the period character (.) so that it matches every character (instead of every character except /n).

IgnorePatternWhitespace

x

Specifies that unescaped white space is excluded from the pattern and enables comments following a number sign (#). (For a list of escaped white-space characters, see Character Escapes.) Note that white space is never eliminated from within a character class.

RightToLeft

N/A

Specifies that the search moves from right to left instead of from left to right. A regular expression with this option moves to the left of the starting position instead of to the right. (Therefore, the starting position should be specified as the end of the string instead of the beginning.) This option cannot be specified in midstream, to prevent the possibility of crafting regular expressions with infinite loops. However, the (?<) lookbehind constructs provide something similar that can be used as a subexpression.

RightToLeft changes the search direction only. It does not reverse the substring that is searched for. The lookahead and lookbehind assertions do not change: lookahead looks to the right; lookbehind looks to the left.

ECMAScript

N/A

Specifies that ECMAScript-compliant behavior is enabled for the expression. This option can be used only in conjunction with the IgnoreCase and Multiline flags. Use of ECMAScript with any other flags results in an exception.

CultureInvariant

N/A

Specifies that cultural differences in language is ignored. See Performing Culture-Insensitive Operations in the RegularExpressions Namespace for more information.

Assertion

Description

^

Specifies that the match must occur at the beginning of the string or the beginning of the line. For more information, see the Multiline option in Regular Expression Options.

$

Specifies that the match must occur at the end of the string, before /n at the end of the string, or at the end of the line. For more information, see the Multiline option in Regular Expression Options.

/A

Specifies that the match must occur at the beginning of the string (ignores the Multiline option).

/Z

Specifies that the match must occur at the end of the string or before /n at the end of the string (ignores the Multiline option).

/z

Specifies that the match must occur at the end of the string (ignores the Multiline option).

/G

Specifies that the match must occur at the point where the previous match ended. When used with Match.NextMatch(), this ensures that matches are all contiguous.

/b

Specifies that the match must occur on a boundary between /w (alphanumeric) and /W (nonalphanumeric) characters. The match must occur on word boundaries — that is, at the first or last characters in words separated by any nonalphanumeric characters.

/B

Specifies that the match must not occur on a /b boundary.

Quantifier

Description

*

Specifies zero or more matches; for example, /w* or (abc)*. Equivalent to {0,}.

+

Specifies one or more matches; for example, /w+ or (abc)+. Equivalent to {1,}.

?

Specifies zero or one matches; for example, /w? or (abc)?. Equivalent to {0,1}.

{n}

Specifies exactly n matches; for example, (pizza){2}.

{n,}

Specifies at least n matches; for example, (abc){2,}.

{n,m}

Specifies at least n, but no more than m, matches.

*?

Specifies the first match that consumes as few repeats as possible (equivalent to lazy *).

+?

Specifies as few repeats as possible, but at least one (equivalent to lazy +).

??

Specifies zero repeats if possible, or one (lazy ?).

{n}?

Equivalent to {n} (lazy {n}).

{n,}?

Specifies as few repeats as possible, but at least n (lazy {n,}).

{n,m}?

Specifies as few repeats as possible between n and m (lazy {n,m}).

Grouping construct

Description

(   )

Captures the matched substring (or noncapturing group; for more information, see the ExplicitCapture option in Regular Expression Options). Captures using () are numbered automatically based on the order of the opening parenthesis, starting from one. The first capture, capture element number zero, is the text matched by the whole regular expression pattern.

(?<name>   )

Captures the matched substring into a group name or number name. The string used for name must not contain any punctuation and it cannot begin with a number. You can use single quotes instead of angle brackets; for example, (?'name').

(?<name1-name2> )

Balancing group definition. Deletes the definition of the previously defined group name2 and stores in group name1 the interval between the previously defined name2 group and the current group. If no group name2 is defined, the match backtracks. Because deleting the last definition of name2 reveals the previous definition of name2, this construct allows the stack of captures for group name2 to be used as a counter for keeping track of nested constructs such as parentheses. In this construct, name1 is optional. You can use single quotes instead of angle brackets; for example, (?'name1-name2').

(?:   )

Noncapturing group.

(?imnsx-imnsx:   )

Applies or disables the specified options within the subexpression. For example, (?i-s: ) turns on case insensitivity and disables single-line mode. For more information, see Regular Expression Options.

(?=   )

Zero-width positive lookahead assertion. Continues match only if the subexpression matches at this position on the right. For example, /w+(?=/d) matches a word followed by a digit, without matching the digit. This construct does not backtrack.

(?!   )

Zero-width negative lookahead assertion. Continues match only if the subexpression does not match at this position on the right. For example, /b(?!un)/w+/b matches words that do not begin with un.

(?<=   )

Zero-width positive lookbehind assertion. Continues match only if the subexpression matches at this position on the left. For example, (?<=19)99 matches instances of 99 that follow 19. This construct does not backtrack.

(?<!   )

Zero-width negative lookbehind assertion. Continues match only if the subexpression does not match at the position on the left.

(?>   )

Nonbacktracking subexpression (also known as a "greedy" subexpression). The subexpression is fully matched once, and then does not participate piecemeal in backtracking. (That is, the subexpression matches only strings that would be matched by the subexpression alone.)

Number

Name

Pattern

0

0 (default name)

((?<One>abc)/d+)?(?<Two>xyz)(.*)

1

1 (default name)

((?<One>abc)/d+)

2

2 (default name)

(.*)

3

One

(?<One>abc)

4

Two

(?<Two>xyz)

Backreference construct

Definition

/number

Backreference. For example, (/w)/1 finds doubled word characters.

/k<name>

Named backreference. For example, (?<char>/w)/k<char> finds doubled word characters. The expression (?<43>/w)/43 does the same. You can use single quotes instead of angle brackets; for example, /k'char'.

Construct

Definition

(?imnsx-imnsx)

Sets or disables options such as case insensitivity to be turned on or off in the middle of a pattern. For information on specific options, see Regular Expression Options. Option changes are effective until the end of the enclosing group. See also the information on the grouping construct (?imnsx-imnsx: ), which is a cleaner form.

(?# )

Inline comment inserted within a regular expression. The comment terminates at the first closing parenthesis character.

# [to end of line]

X-mode comment. The comment begins at an unescaped # and continues to the end of the line. (Note that the x option or the RegexOptions.IgnorePatternWhitespace enumerated option must be activated for this kind of comment to be recognized.)