Regular Expression Character Escapes .NET Escaped Character Examples See also Source/Reference
Regular Expression Character Escapes
The backslash character, \, used in regular expression for character escapes can be used to indicate the following character either is a special character, or should be interpreted literally.
to represent a non-print character. e.g. \a, \b, \e, \f, \n, \r, \t, \v.
to represent an ASCII character of two or three digits octal character code, e.g. =\40
to represent a typical character code with specific code followed. e.g. =\x20=\u0020, chr(7)=\cG
to represent a special regular expression element. e.g. \., \$, \^, \{, \[, \(, \|, \), \*, \+, \?, \\.
In general, character escapes are recognized in regular expression patterns but not in replacement patterns.
.NET Escaped Character
Escaped Character
Description
Exception
\a
Matches a bell or alarm character, \u0007.
\b
In a [character_group] character class, matches a backspace, \u0008.
Outside a character class, \b is an anchor that matches a word boundary.
\e
Matches an escape, \u001B.
\f
Matches a form feed, \u000C.
\n
Matches a new line, \u000A.
\r
Matches a carriage return, \u000D.
\t
Matches a tab, \u0009.
\v
Matches a vertical tab, \u000B.
\nnn
Matches an ASCII character, where nnn consists of two or three digits that represent the octal character code.
This construct is interpreted as a backreference if it has only one digit or if it corresponds to the number of a capturing group.
\xnn
Matches an ASCII character, where nn is a exactly two-digit hexadecimal character code.
\cX, \cx
Matches the ASCII control character that is specified by X or x, where X or x is the letter of the control character.
\unnnn
Matches a Unicode character where nnnn is a exactly four-digit hexadecimal UTF-16 code unit. The Perl 5 character escape that is used to specify Unicode is not supported by .NET. The Perl 5 character escape has the form \x{####…}, where ####… is a series of hexadecimal digits.
\., \$, \^, \{, \[, \(, \|, \), \*, \+, \?, \\
to match characters ., $, ^, {, [, (, |, ), *, +, ?, and \ respectilvely.
However, these special regular expression elements can also be included in a positive character group.
Examples
Examples of Character Escapes
ASP.NET Code Input:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<title>Sample Page</title>
<meta http-equiv="Content-Type" content="text/html;charset=utf-8">
<script runat="server">
Sub Page_Load()
Dim xstring As String
Dim xmatchstr As String = ""
xstring = Chr(7)&Chr(8)&Chr(27)&Chr(12)&Chr(10)&CHR(13)&Chr(9)&Chr(11)
xmatchstr = xmatchstr & "Given string: " & "Chr(7)&Chr(8)&Chr(27)&Chr(12)&Chr(10)&CHR(13)&Chr(9)&Chr(11)"
xmatchstr = xmatchstr & showresult(xstring,"\a[\b]\e\f\n\r\t\v")
xstring = Chr(7)&Chr(8)&Chr(7)&Chr(7)&Chr(10)
xmatchstr = xmatchstr & "<br />Given string: " & "Chr(7)&Chr(8)&Chr(7)&Chr(7)&Chr(10)"
xmatchstr = xmatchstr & showresult(xstring,"\07\x08\cg\cG\u000A")
xstring = ".$^{[(|)*+?\.$^{[(|)*+?\"
xmatchstr = xmatchstr & "<br />Given string: """ & ".$^{[(|)*+?\.$^{[(|)*+?\"""
xmatchstr = xmatchstr & showresult(xstring,"\.\$\^\{\[\(\|\)\*\+\?\\[.][$][\^][{][\[][(][|][)][*][+][?][\\]")
lbl01.Text = xmatchstr
End Sub
Function showresult(xstring,xpattern)
Dim xmatch As Match
Dim xcaptures As CaptureCollection
Dim xmatchstr As String = ""
Dim xint As Integer
xmatchstr = xmatchstr & "<br />Result of Regex.Match(string,""" & xpattern & """): """
xmatch = Regex.Match(xstring,xpattern)
xmatchstr = xmatchstr & xmatch.value & """<br />"
xcaptures = xmatch.Captures
xmatchstr = xmatchstr & "->Result of CaptureCollection.Count: """
xmatchstr = xmatchstr & xcaptures.Count & """<br />"
For xint = 0 to xcaptures.Count - 1
xmatchstr = xmatchstr & "->->Result of CaptureCollection("& xint & ").Value, Index, Length: """
xmatchstr = xmatchstr & xcaptures(xint).Value & ", " & xcaptures(xint).Index & ", " & xcaptures(xint).Length & """<br />"
Next
Return xmatchstr
End Function
</script>
</head>
<body>
<% Response.Write ("<h1>This is a Sample Page of Escaped Character</h1>") %>
<p>
<%-- Set on Page_Load --%>
<asp:Label id="lbl01" runat="server" />
</p>
</body>
</html>