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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)&amp;Chr(8)&amp;Chr(27)&amp;Chr(12)&amp;Chr(10)&amp;CHR(13)&amp;Chr(9)&amp;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)&amp;Chr(8)&amp;Chr(7)&amp;Chr(7)&amp;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>
HTML Web Page Embedded Output:

See also

  • Regular Expression Language - Quick Reference

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

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ID: 190700025 Last Updated: 7/25/2019 Revision: 0 Ref:

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References

  1. Active Server Pages,  , http://msdn.microsoft.com/en-us/library/aa286483.aspx
  2. ASP Overview,  , http://msdn.microsoft.com/en-us/library/ms524929%28v=vs.90%29.aspx
  3. ASP Best Practices,  , http://technet.microsoft.com/en-us/library/cc939157.aspx
  4. ASP Built-in Objects,  , http://msdn.microsoft.com/en-us/library/ie/ms524716(v=vs.90).aspx
  5. Response Object,  , http://msdn.microsoft.com/en-us/library/ms525405(v=vs.90).aspx
  6. Request Object,  , http://msdn.microsoft.com/en-us/library/ms524948(v=vs.90).aspx
  7. Server Object (IIS),  , http://msdn.microsoft.com/en-us/library/ms525541(v=vs.90).aspx
  8. Application Object (IIS),  , http://msdn.microsoft.com/en-us/library/ms525360(v=vs.90).aspx
  9. Session Object (IIS),  , http://msdn.microsoft.com/en-us/library/ms524319(8v=vs.90).aspx
  10. ASPError Object,  , http://msdn.microsoft.com/en-us/library/ms524942(v=vs.90).aspx
  11. ObjectContext Object (IIS),  , http://msdn.microsoft.com/en-us/library/ms525667(v=vs.90).aspx
  12. Debugging Global.asa Files,  , http://msdn.microsoft.com/en-us/library/aa291249(v=vs.71).aspx
  13. How to: Debug Global.asa files,  , http://msdn.microsoft.com/en-us/library/ms241868(v=vs.80).aspx
  14. Calling COM Components from ASP Pages,  , http://msdn.microsoft.com/en-us/library/ms524620(v=VS.90).aspx
  15. IIS ASP Scripting Reference,  , http://msdn.microsoft.com/en-us/library/ms524664(v=vs.90).aspx
  16. ASP Keywords,  , http://msdn.microsoft.com/en-us/library/ms524672(v=vs.90).aspx
  17. Creating Simple ASP Pages,  , http://msdn.microsoft.com/en-us/library/ms524741(v=vs.90).aspx
  18. Including Files in ASP Applications,  , http://msdn.microsoft.com/en-us/library/ms524876(v=vs.90).aspx
  19. ASP Overview,  , http://msdn.microsoft.com/en-us/library/ms524929(v=vs.90).aspx
  20. FileSystemObject Object,  , http://msdn.microsoft.com/en-us/library/z9ty6h50(v=vs.84).aspx
  21. http://msdn.microsoft.com/en-us/library/windows/desktop/ms675944(v=vs.85).aspx,  , ADO Object Model
  22. ADO Fundamentals,  , http://msdn.microsoft.com/en-us/library/windows/desktop/ms680928(v=vs.85).aspx
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