Use regular expressions in Visual Studio

Visual Studio uses .NET regular expressions to find and replace text.

Regular expression examples

The following table contains some regular expression characters, operators, constructs, and pattern examples. For a more complete reference, see Regular expression language.

Purpose Expression Example
Match any single character (except a line break). For more information, see Any character. . a.o matches "aro" in "around" and "abo" in "about" but not "acro" in "across"
Match zero or more occurrences of the preceding expression (match as many characters as possible). For more information, see Match zero or more times. * a*r matches "r" in "rack", "ar" in "ark", and "aar" in "aardvark"
Match any character zero or more times. .* c.*e matches "cke" in "racket", "comme" in "comment", and "code" in "code"
Match one or more occurrences of the preceding expression (match as many characters as possible). For more information, see Match one or more times. + e+d matches "eed" in "feeder" and "ed" in "faded"
Match any character one or more times. .+ e.+e matches "eede" in "feeder" but finds no matches in "feed"
Match zero or more occurrences of the preceding expression (match as few characters as possible). For more information, see Match zero or more times (lazy match). *? \w*?d matches "fad" and "ed" in "faded" but not the entire word "faded" due to the lazy match
Match one or more occurrences of the preceding expression (match as few characters as possible). For more information, see Match one or more times (lazy match). +? e\w+? matches "ee" in "asleep" and "ed" in "faded" but finds no matches in "fade"
Anchor the match string to the beginning of a line or string ^ ^car matches the word "car" only when it appears at the beginning of a line
Anchor the match string to the end of a line \r?$ car\r?$ matches "car" only when it appears at the end of a line
Anchor the match string to the end of the file $ car$ matches "car" only when it appears at the end of the file
Match any single character in a set [abc] b[abc] matches "ba", "bb", and "bc"
Match any character in a range of characters [a-f] be[n-t] matches "bet" in "between", "ben" in "beneath", and "bes" in "beside", but finds no matches in "below"
Capture and implicitly number the expression contained within parenthesis () ([a-z])X\1 matches "aXa"and "bXb", but not "aXb". "\1" refers to the first expression group "[a-z]". For more information, see Capture groups and replacement patterns.
Invalidate a match (?!abc) real(?!ity) matches "real" in "realty" and "really" but not in "reality." It also finds the second "real" (but not the first "real") in "realityreal".
Match any character that is not in a given set of characters. For more information, see Negative character group. [^abc] be[^n-t] matches "bef" in "before", "beh" in "behind", and "bel" in "below", but finds no matches in "beneath"
Match either the expression before or the one after the symbol | (sponge|mud) bath matches "sponge bath" and "mud bath"
Escape the character following the backslash \ \^ matches the character ^
Specify the number of occurrences of the preceding character or group. For more information, see Match exactly n times. {n}, where 'n' is the number of occurrences x(ab){2}x matches "xababx"
x(ab){2,3}x matches "xababx" and "xabababx" but not "xababababx"
Match text in a Unicode category. For more information about Unicode character classes, see Unicode Standard 5.2 Character Properties. \p{X}, where "X" is the Unicode number. \p{Lu} matches "T" and "D" in "Thomas Doe"
Match a word boundary \b (Outside a character class \b specifies a word boundary, and inside a character class \b specifies a backspace.) \bin matches "in" in "inside" but finds no matches in "pinto"
Match a line break (that is, a carriage return followed by a new line) \r?\n End\r?\nBegin matches "End" and "Begin" only when "End" is the last string in a line and "Begin" is the first string in the next line
Match any word character \w a\wd matches "add" and "a1d" but not "a d"
Match any whitespace character \s Public\sInterface matches the phrase "Public Interface"
Match any decimal digit character \d \d matches "4" and "0" in "wd40"

An example regular expression that combines some of the operators and constructs to match a hexadecimal number is \b0[xX]([0-9a-fA-F]+\)\b. This expression matches "0xc67f" but not "0xc67g".

Tip

In Windows operating systems, most lines end in "\r\n" (a carriage return followed by a new line). These characters aren't visible but are present in the editor and passed to the .NET regular expression service.

Capture groups and replacement patterns

A capture group delineates a subexpression of a regular expression and captures a substring of an input string. You can use captured groups within the regular expression itself (for example, to look for a repeated word), or in a replacement pattern. For detailed information, see Grouping constructs in regular expressions.

To create a numbered capture group, surround the subexpression with parentheses in the regular expression pattern. Captures are numbered automatically from left to right based on the position of the opening parenthesis in the regular expression. To access the captured group:

  • within the regular expression: Use \number. For example, \1 in the regular expression (\w+)\s\1 references the first capture group (\w+).

  • in a replacement pattern: Use $number. For example, the grouped regular expression (\d)([a-z]) defines two groups: the first group contains a single decimal digit, and the second group contains a single character between a and z. The expression finds four matches in the following string: 1a 2b 3c 4d. The replacement string z$1 references the first group only ($1), and converts the string to z1 z2 z3 z4.

The following image shows a regular expression (\w+)\s\1 and a replacement string $1. Both the regular expression and the replacement pattern reference the first capture group that's automatically numbered 1. When you choose Replace all in the Quick Replace dialog box in Visual Studio, repeated words are removed from the text.

Quick Replace showing a numbered capture group in Visual Studio

Tip

Make sure the Use Regular Expressions button is selected in the Quick Replace dialog box.

Named capture groups

Instead of relying on the automatic numbering of a capture group, you can give it a name. The syntax for a named capture group is (?<name>subexpression).

Named capture groups, like numbered capture groups, can be used within the regular expression itself or in a replacement pattern. To access the named capture group:

  • within the regular expression: Use \k<name>. For example, \k<repeated> in the regular expression (?<repeated>\w+)\s\k<repeated> references the capture group that's named repeated and whose subexpression is \w+.

  • in a replacement pattern: Use ${name}. For example, ${repeated}.

As an example, the following image shows a regular expression (?<repeated>\w+)\s\k<repeated> and a replacement string ${repeated}. Both the regular expression and the replacement pattern reference the capture group named repeated. When you choose Replace all in the Quick Replace dialog box in Visual Studio, repeated words are removed from the text.

Quick Replace showing a named capture group in Visual Studio

Tip

Make sure the Use Regular Expressions button is selected in the Quick Replace dialog box.

For more information about named capture groups, see Named matched subexpressions. For more information about regular expressions that are used in replacement patterns, see Substitutions in regular expressions.

See also