Develop Reference

How do I escape a backslash in the following regex c#

Here is my function, I'm trying to replace a string in a file, but c# tells me my regex is malformed. Any ideas?
public void function(string fileName, string path) {
string pathToAmmend = #"$SERVERROOT\pathpath";
string newPath = #"$SERVERROOT\" + path;
File.WriteAllText(fileName, Regex.Replace(File.ReadAllText(fileName), pathToAmmend, newPath));
....
}
It works if i change the strings to:
string pathToAmmend = #"$SERVERROOT\\pathpath";
string newPath = #"$SERVERROOT\\" + path;
But then I have two slashes and I only want one slash.

It sounds like you don't actually need a regular expression at all. It sounds like you quite possibly just want string.Replace:
// Split into three statements for clarity.
string input = File.ReadAllText(fileName);
string output = input.Replace(pathToAmend, newPath);
File.WriteAllText(output);
Only use regular expressions when you're genuinely trying to match patterns.

A \ is a special escaping character in regular expressions. You have to escape it so that it will be interpreted as a literal \ and not an escape sequence. $ is also a special character (an end anchor), so you'll want to escape that as well.
string pathToAmmend = #"\$SERVERROOT\\pathpath";
Using # to create a verbatim string only means you don't have to escape the \ for the sake of the C# compiler. You still have escape the \ for in a regular expression pattern. Without the verbatim string this would be:
string pathToAmmend = "\\$SERVERROOT\\\\pathpath";
Of course, as Jon Skeet points out, for something this simple, regular expressions aren't really the best way to go here.

How to use " in a String with a path?

I have a String with a path in it.
It looks like this :
TaskManager = "RegistryKey objRegistryKey = Registry.CurrentUser.CreateSubKey("Software\\Microsoft\\Windows\\CurrentVersion\\Policies\\System");"
I want to use this string to compile with codedom, but I get an error saying "cant find Software\Microsoft......".
Is there anyway to replace the " with another char?

I use verbatim string literal for paths so I don't have to double the backslashes:
TaskManager = #"RegistryKey objRegistryKey = Registry.CurrentUser.CreateSubKey(""Software\Microsoft\Windows\CurrentVersion\Policies\System"");"
" is doubled ""

to write " inside a string use \"
String str= "my string with \"quotes\""; // my string with "quotes"
the character \ is used to write special character inside a string for example a \t write inside the string a tab and \n make the string go to a new line
or
String str= #"my string with ""quotes"""; //same as before
the character # before a string make the compiler take the string as is, every special character is written without having to use \ before it, the only character that need to be escaped are the quotes itself that you write by doubling them ""
Watch out that iff you use the method with # your \ \ in the path become \

If you are trying to escape the qoute then do something like this:
TaskManager = "RegistryKey objRegistryKey = Registry.CurrentUser.CreateSubKey(\"Software\\Microsoft\\Windows\\CurrentVersion\\Policies\\System\");"

Use \"
to get a double quote, the same way as you used \ to get a backslash.

TaskManager = "RegistryKey objRegistryKey = Registry.CurrentUser.CreateSubKey(\"Software\\Microsoft\\Windows\\CurrentVersion\\Policies\\System\");"
That should fix it.

you can use it this way
TaskManager = "RegistryKey objRegistryKey = Registry.CurrentUser.CreateSubKey('Software\\Microsoft\\Windows\\CurrentVersion\\Policies\\System');"

Replacing double backwards slashes with single ones in c#

I need to replace double quotes with single so that something like this
\\\\servername\\dir1\\subdir1\\
becomes
\\servername\dir1\subdir1\
I tried this
string dir = "\\\\servername\\dir1\\subdir1\\";
string s = dir.Replace(#"\\", #"\");
The result I get is
\\servername\\dir1\\subdir1\\
Any ideas?

You don't need to replace anything here. The backslashes are escaped, that's why they are doubled.
Just like \t represents a tabulator, \\ represents a single \. You can see the full list of Escape Sequences on MSDN.
string dir = "\\\\servername\\dir1\\subdir1\\";
Console.WriteLine(dir);
This will output \\servername\dir1\subdir1\.
BTW: You can use the verbatim string to make it more readable:
string dir = #"\\servername\dir1\subdir1\";

There is no problem with the code for replacing. The result that you get is:
\servername\dir1\subdir1\
When you are looking at the result in the debugger, it's shown as it would be written as a literal string, so a backslash characters is shown as two backslash characters.
The string that you create isn't what you think it is. This code:
string dir = "\\\\servername\\dir1\\subdir1\\";
produces a string containing:
\\servername\dir1\subdir1\
The replacement code does replace the \\ at the beginning of the string.
If you want to produce the string \\\\servername\\dir1\\subdir1\\, you use:
string dir = #"\\\\servername\\dir1\\subdir1\\";
or:
string dir = "\\\\\\\\servername\\\\dir1\\\\subdir1\\\\";

This string "\\\\servername\\dir1\\subdir1\\" is the same as #"\\servername\dir1\subdir1\". In order to escape backslashes you need either use # symbol before string, or use double backslash instead of one.
Why you need that? Because in C# backslash used for escape sequences.

Problem with String Verbatim

I use C#.
I need assign a value to a string as verbatim.
Here my code:
string verbatim = "#<META NAME="ROBOTS" CONTENT="NOINDEX, NOFOLLOW">";
or
string verbatim = #"<META NAME=""ROBOTS"" CONTENT=""NOINDEX, NOFOLLOW"">";
But it does not work.
What I'm doing wrong here? Thanks

You mean a verbatim string literal? Double-up the internal quotes and move the #:
string verbatim = #"<META NAME=""ROBOTS"" CONTENT=""NOINDEX, NOFOLLOW"">";

The # charctaer goes outside the string ath beginning and you need to escape your quotes, i.e.
string verbatim = #"<META NAME=""ROBOTS"" CONTENT=""NOINDEX, NOFOLLOW"">"

The # must be outside the string and you need to use double quotes:
string verbatim = #"<META NAME=""ROBOTS"" CONTENT=""NOINDEX, NOFOLLOW"">";

How to create a string with special characters in C#

How can I create a string which contains the following:
<Object type="System.Windows.Forms.Form

Use an escape character for the quote:
string temp = "<Object type=\"System.Windows.Forms.Form"
See the msdn article for more examples:
http://msdn.microsoft.com/en-us/library/h21280bw.aspx
Edit
Correct link for C#: C# programming guide

You have two choices, depending on the remainder of the text you want to place into the string:
use the escape character \ within the double-quoted string for any double-quote marks, as the other answers have suggested.
string s = "<Object type=\"System.Windows.Forms.Form";
use the string-# form, which avoids processing the \ (such as in path names like C:\Temp\Myfile.txt), and then double the double-quote:
string s = #"<Object type=""System.Windows.Forms.Form";
See also: http://msdn.microsoft.com/en-us/library/362314fe(v=vs.71).aspx

You can use the backslash character to escape strings, the example below should fit your needs:
Example:
string test = "<Object type=\"System.Windows.Forms.Form";
MSDN Specification on String Literals / Escaping Literals:
MSDN : String Literals

string s = "<Object type=\"System.Windows.Forms.Form";
Is that what you mean?

var str = "<Object type=\"System.Windows.Forms.Form";

Use backslash to escape.
String str = "<Object type=\"System.Windows.Forms.Forms";