Regular Expression in Dot Net Framework Part I - Character Escapes and Character Classes

A regular expression is a pattern that the regular expression engine attempts to match in input text. A pattern consists of one or more character literals, operators, or constructs.

Each section in this quick reference lists a particular category of characters, operators, and constructs that you can use to define regular expressions:

Character escapes
Character classes
Anchors
Grouping constructs
Quantifiers
Backreference constructs
Alternation constructs
Substitutions
Regular expression options
Miscellaneous constructs

Character Escapes

The backslash character (\) in a regular expression indicates that the character that follows it either is a special character (as shown in the following table), or should be interpreted literally.

Escaped character	Description	Pattern	Matches
\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"
\ nnn	Uses octal representation to specify a character (nnn consists of two or three digits).	\w\040\w	"a b", "c d" in "a bc d"
\x nn	Uses hexadecimal representation to specify a character (nn consists of exactly two digits).	\w\x20\w	"a b", "c d" in "a bc d"
\c X \c x	Matches the ASCII control character that is specified by X or x, where X or x is the letter of the control character.	\cC	"\x0003" in "\x0003" (Ctrl-C)
\u nnnn	Matches a Unicode character by using hexadecimal representation (exactly four digits, as represented by nnnn).	\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, and \. is the same as \x2E. 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 Classes

A character class matches any one of a set of characters. Character classes include the language elements listed in the following table.

Character class	Description	Pattern	Matches
[ 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. To match a literal period character (. or \u002E), you must precede it with the escape character (\.).	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 character other than a decimal digit.	\D	" ", "=", " ", "I", "V" in "4 = IV"