Regular Expression Character Classes

Instead of using a single character or escaped character, a character class is a set of characters that is used to match against an input string.

• a symbol is used to represent a set of characters. e.g. "."=any character.
• escaped character classes to represent a group of specific charcters. e.g. \p{unicode name,\P{unicode name}, \w, \W, \s, \S, \d, \D
• a pair square brackets, [], is used to specify a set of characters, e.g. [abc]=a or b or c
  • a hyphen character, -, is used as a range separator unless it is the first or last character of the group. e.g. [a-c]=a or b or c
  • a leading caret character, ^, is used to specify a negative sense that the set of characters must not appear in an input string. e.g. [^abc]=not (a and b and c)
  • a hyphen character, -, is used to indicate a nested excluded group from the base group. e.g. [a-c-[b]]=a or b.

.NET Any Character, .

The period character, ., is used to match any character including the carriage return character, \r or \u000D except the newline character, \n or \u000A. But in a character class, a period, ., is treated as a literal period character.

Escaped Character Class \

The backslash character, \, used in regular expression for character class can be used to indicate the following character classes.

.NET Unicode category or Unicode block: \p{name}

The backslash character, \, followed by the character p is used to indicate a Unicode general category or named block by specifing the name with the category abbreviation or named block name that any one of which may be used to match an input string..

.NET Negative Unicode category or Unicode block: \P{name}

The backslash character, \, followed by the character P is used to indicate a Unicode general category or named block by specifing the name with the category abbreviation or named block name that cannot appear in an input string.

.NET Word Character: \w

The backslash character, \, followed by the character w is used to indicate a set of word characters that any one of which may be used to match an input string.  By default, the set of word characters are members of the predefined Unicode categories. In other words, \w is equivalent to [\p{Ll}\p{Lu}\p{Lt}\p{Lo}\p{Nd}\p{Pc}\p{Lm}]. If ECMAScript-compliant behavior is specified, \w is equivalent to [a-zA-Z_0-9].

.NET Non-word Character: \W

The backslash character, \, followed by the character W is used to indicate a set of word characters that cannot appear in an input string. By default, the set of word characters are members of the predefined Unicode categories. In other words, \W is equivalent to [^\p{Ll}\p{Lu}\p{Lt}\p{Lo}\p{Nd}\p{Pc}\p{Lm}]. If ECMAScript-compliant behavior is specified, \W is equivalent to [^a-zA-Z_0-9].

.NET Whitespace Character: \s

The backslash character, \, followed by the character s is used to indicate a set of whitespace characters that any one of which may be used to match an input string.  By default, the set of whitespace characters are members of the predefined escape sequences and Unicode categories. In other words, \s is equivalent to [\f\n\r\t\v\x85\p{Z}]. If ECMAScript-compliant behavior is specified, \s is equivalent to [ \f\r\r\t\v].

.NET Non-whitespace Character: \S

The backslash character, \, followed by the character S is used to indicate a set of whitespace characters that cannot appear in an input string. By default, the set of whitespace characters are members of the predefined escape sequences and Unicode categories. In other words, \S is equivalent to [^\f\n\r\t\v\x85\p{Z}]. If ECMAScript-compliant behavior is specified, \S is equivalent to [^ \f\r\r\t\v].

.NET Decimal Digit Character: \d

The backslash character, \, followed by the character d is used to indicate a set of decimal digit characters that any one of which may be used to match an input string. By default, the set of decimal digit characters are members of the predefined Unicode categories. In other words, \d is equivalent to [\p{Nd}]. If ECMAScript-compliant behavior is specified, \d is equivalent to [0-9].

.NET Non-decimal Digit Character: \D

The backslash character, \, followed by the character D is used to indicate a set of decimal digit characters that cannot appear in an input string. By default, the set of decimal digit characters are members of the predefined Unicode categories. In other words, \D is equivalent to [\P{Nd}]. If ECMAScript-compliant behavior is specified, \D is equivalent to [^0-9].

Character Group, []

.NET Positive Character Group, []

A pair of square brackets is used to specify a set of characters that any one of which may be used to match an input string. The set of characters may be specified individually, as a range, or both.

• [*character_group*]: character_group can consist of any combination of one or more literal characters, escape characters, or character classes.
• [*firstCharacter*-*lastCharacter*]: firstCharacter is the character that begins the range and lastCharacter is the character that ends the range. Two characters are contiguous if they have adjacent Unicode code points. firstCharacter must be the character with the lower code point, and lastCharacter must be the character with the higher code point. A hyphen character, -, is always interpreted as the range separator unless it is the first or last character of the group.

.NET Negative Character Group, [^]

A pair of square brackets with leading caret is used to specify a set of characters that cannot appear in an input string. The set of characters may be specified individually, as a range, or both.

• [*^character_group*]: the leading caret, ^, is used to indicate a negative charactergroup. character_group can consist of any combination of one or more literal characters, escape characters, or character classes that cannot appear in an input string..
• [^*firstCharacter*-*lastCharacter*]: the leading caret, ^, is used to indicate a negative charactergroup. firstCharacter is the character that begins the range and lastCharacter is the character that ends the range. Two characters are contiguous if they have adjacent Unicode code points. firstCharacter must be the character with the lower code point, and lastCharacter must be the character with the higher code point. A hyphen character, -, is always interpreted as the range separator unless it is the first or last character of the group.

A negative character group in a larger regular expression pattern is not a zero-width assertion. That is, after evaluating the negative character group, the regular expression engine advances one character in the input string.

.NET Character Subtraction Group, [base_group-[excluded_group]]

A character subtraction group is used to specify a set of characters through subtraction that any one of which may be used to match an input string. The set of character subtraction group is the result of excluding the characters in a base character group from another character excluded group.

The form of character subtraction group is [base_group-[excluded_group]]. The hyphen, -, is used to indicate the following nested group is an character excluded_group.

Supported Unicode

Supported Unicode General Categories  Supported Named Blocks

See also

• Regular Expression Language - Quick Reference

Examples

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
    <head>
       <title>Sample Page</title>
       <meta http-equiv="Content-Type" content="text/html;charset=utf-8">
       <script runat="server">
           Sub Page_Load()
               Dim xstring As String = "01 345"&ChrW(913)&"67 9abc def"&Chr(13)&Chr(10)&"7890"&Chr(13)&Chr(10)
               Dim xmatchstr As String = ""
               Dim xoption As RegexOptions = RegexOptions.Multiline
               xmatchstr = xmatchstr & "Given string: " & """01 345""&amp;ChrW(913)&amp;""67 9abc def""&amp;Chr(13)&amp;Chr(10)&amp;""7890""&amp;Chr(13)&amp;Chr(10)" & "<br />"
               xmatchstr = xmatchstr & showresult(xstring,".+",RegexOptions.None)
               xmatchstr = xmatchstr & showresult(xstring,"\P{Ll}",RegexOptions.None)
               xmatchstr = xmatchstr & showresult(xstring,"\p{Ll}",RegexOptions.None)
               xmatchstr = xmatchstr & showresult(xstring,"\p{IsBasicLatin}",RegexOptions.None)
               xmatchstr = xmatchstr & showresult(xstring,"\P{IsBasicLatin}",RegexOptions.None)
               xmatchstr = xmatchstr & showresult(xstring,"\w",RegexOptions.None)
               xmatchstr = xmatchstr & showresult(xstring,"\W",RegexOptions.None)
               xmatchstr = xmatchstr & showresult(xstring,"\s",RegexOptions.None)
               xmatchstr = xmatchstr & showresult(xstring,"\S",RegexOptions.None)
               xmatchstr = xmatchstr & showresult(xstring,"\d",RegexOptions.None)
               xmatchstr = xmatchstr & showresult(xstring,"\D",RegexOptions.None)
               xmatchstr = xmatchstr & showresult(xstring,"[1357\r]",RegexOptions.None)
               xmatchstr = xmatchstr & showresult(xstring,"[^1357\r]",RegexOptions.None)
               xmatchstr = xmatchstr & showresult(xstring,"[1357\r-[5]]",RegexOptions.None)
               xmatchstr = xmatchstr & showresult(xstring,"[^1357\r-[5]]",RegexOptions.None)
               lbl01.Text = xmatchstr
           End Sub
           Function showresult(xstring,xpattern,xoption)
               Dim xmatches As MatchCollection
               Dim xmatchstr As String = ""
               Dim xint As Integer
               xmatchstr = xmatchstr & "<br />Result of Regex.Matches(string,""" & xpattern & """," & xoption & "): "
               xmatches = Regex.Matches(xstring,xpattern,xoption)
               xmatchstr = xmatchstr & "<br />->Result of MatchCollection.Count: """
               xmatchstr = xmatchstr & xmatches.Count & """<br />"
               For xint = 0 to xmatches.Count - 1
                   xmatchstr = xmatchstr & "->->Result of MatchCollection("& xint & ").Value, Index, Length: """
                   xmatchstr = xmatchstr & xmatches(xint).Value & ", " & xmatches(xint).Index & ", " & xmatches(xint).Length & """<br />"
               Next
               Return xmatchstr
           End Function
       </script>
    </head>
    <body>
       <% Response.Write ("<h1>This is a Sample Page of Character Classes</h1>") %>
       <p>
           <%-- Set on Page_Load --%>
           <asp:Label id="lbl01" runat="server" />
       </p>
    </body>
</html>

Source/Reference

• https://docs.microsoft.com/en-us/dotnet/standard/base-types/regular-expression-language-quick-reference
• https://docs.microsoft.com/en-us/dotnet/standard/base-types/character-escapes-in-regular-expressions