Character Escapes

Character Escapes

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Microsoft Visual Studio 2008/.NET Framework 3.5

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.NET Framework Developer's Guide

Character Escapes

Most of the important regular expression language operators are unescaped single characters. The escape character \ (a single backslash) signals to the regular expression parser that the character following the backslash is not an operator. For example, the parser treats an asterisk (*) as a repeating quantifier and a backslash followed by an asterisk (\*) as the Unicode character 002A.

The character escapes listed in this table are recognized both in regular expressions and in replacement patterns.

Escaped character	Description
ordinary characters	Characters other than . $ ^ { [ ( \| ) * + ? \ match themselves.
\a	Matches a bell (alarm) \u0007.
\b	Matches a backspace \u0008 if in a [] character class; otherwise, see the note following this table.
\t	Matches a tab \u0009.
\r	Matches a carriage return \u000D. Note that \r is not equivalent to the newline character, \n.
\v	Matches a vertical tab \u000B.
\f	Matches a form feed \u000C.
\n	Matches a new line \u000A.
\e	Matches an escape \u001B.
\040	Matches an ASCII character as octal (up to three digits); numbers with no leading zero are backreferences if they have only one digit or if they correspond to a capturing group number. (For more information, see Backreferences.) For example, the character \040 represents a space.
\x20	Matches an ASCII character using hexadecimal representation (exactly two digits).
\cC	Matches an ASCII control character; for example, \cC is control-C.
\u0020	Matches a Unicode character using hexadecimal representation (exactly four digits). Note: The Perl 5 character escape that is used to specify Unicode is not supported by the .NET Framework. The Perl 5 character escape is of the form \x{####…}, where "####…" is a series of hexadecimal digits. Instead, use the .NET Framework character escape described in this row.
\	When followed by a character that is not recognized as an escaped character, matches that character. For example, \* is the same as \x2A.

Note:
The escaped character \b is a special case. In a regular expression, \b denotes a word boundary (between \w and \W characters) except within a [] character class, where \b refers to the backspace character. In a replacement pattern, \b always denotes a backspace.

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Regular Expression Language Elements

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Character escapes not recognized in replacement patterns

ChernoJ | Edit | Show History

Contrary to the documentation here, character escapes in replacement patterns don't get translated to the corresponding character upon replace.

Eg:

Regex.Replace("abcDEFghi", "(DEF)", @"\t")

Expected: abc ghi

Actual: abc\tghi

Repro's on Visual Studio 2008, C#, .Net 3.5.

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String Literals

CLovegren | Edit | Show History

From http://msdn.microsoft.com/en-us/library/aa691090(VS.71).aspx:
A verbatim string literal consists of an @ character followed by a double-quote character, zero or more characters, and a closing double-quote character. A simple example is @"hello". In a verbatim string literal, the characters between the delimiters are interpreted verbatim

string c = "hello \t world";               // hello     world
string d = @"hello \t world";               // hello \t world

Drop the at (@) from your code and you should be fine.

using System.Text.RegularExpressions;
class test {
 static void Main() {
  System.Console.WriteLine( Regex.Replace( "abcDEFghi", "(DEF)", "\t" ) );
 }
}

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Not a string literals issue...

ChernoJ | Edit | Show History

Dropping the @ would be fine if I wanted a tab character embedded in the string. However, this documentation suggests that the '\' character followed by the 't' character inside a replacement pattern has special meaning, but it doesn't treat it that way.

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