I am trying to replace a string using regex, however I can't seem to find a way to escape the single backslashes for the regex with the double backslashes of the string.
My string literal (this is being read from a text file, as is)
-s \"t\"
and I want to replace it with (again, as a string literal)
-s \"n\"
The best I have been able to come up with is
schedule = Regex.Replace(schedule, "-s\s\\\"\w\\\"", "-s \\\"n\\\"");
The middle argument doesn't compile though, because of the single and double backslashes. It will accept one or the other, but not both (regardless of weather I use #).
I don't use regexes that much so it may be a simple one but I'm pretty stuck!
Thanks
The problem is happening because \ have a special meaning both for strings and regular expressions so it normally needs to be double escaped unless you use # and added to the problem here is the presence of " itself inside the string which needs to be escaped.
Try the following:
schedule = Regex.Replace(schedule, #"-s\s\\""\w\\""", #"-s \""n\""");
After using #, \ doesn't have a special meaning inside strings, but it still have a special meaning inside regular expression expression so it needs to be escaped only once if it is needed literally.
Also now you need to use "" to escape " inside the string (how would you escape it otherwise, since \ doesn't have a special meaning anymore).
This works:
var schedule = #"-s \""t\""";
// value is -s \"t\"
schedule = Regex.Replace(schedule, #"-s\s\\""\w\\""", #"-s \""n\""");
// value is -s \"n\"
The escaping is complicated because \ and " have special meanings both in how you encode strings in C# and in regex. The search pattern is (without any escaping) the C# string -s\s\\"\w\\", which tells regex to look for a literal \ and a literal ". The replacement string is -s \"n\", because you don't need to escape the backslashes in a replacement string.
You could, of course, write this with normal strings ("...") instead of verbatim strings (#"..."), but it'd get way messier.
Related
I want to write something like this C:\Users\UserName\Documents\Tasks in a textbox:
txtPath.Text = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments)+"\Tasks";
I get the error:
Unrecognized escape sequence.
How do I write a backslash in a string?
The backslash ("\") character is a special escape character used to indicate other special characters such as new lines (\n), tabs (\t), or quotation marks (\").
If you want to include a backslash character itself, you need two backslashes or use the # verbatim string:
var s = "\\Tasks";
// or
var s = #"\Tasks";
Read the MSDN documentation/C# Specification which discusses the characters that are escaped using the backslash character and the use of the verbatim string literal.
Generally speaking, most C# .NET developers tend to favour using the # verbatim strings when building file/folder paths since it saves them from having to write double backslashes all the time and they can directly copy/paste the path, so I would suggest that you get in the habit of doing the same.
That all said, in this case, I would actually recommend you use the Path.Combine utility method as in #lordkain's answer as then you don't need to worry about whether backslashes are already included in the paths and accidentally doubling-up the slashes or omitting them altogether when combining parts of paths.
To escape the backslash, simply use 2 of them, like this:
\\
If you need to escape other things, this may be helpful..
There is a special function made for this Path.Combine()
var folder = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);
var fullpath = path.Combine(folder,"Tasks");
Just escape the "\" by using + "\\Tasks" or use a verbatim string like #"\Tasks"
txtPath.Text = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments)+"\\\Tasks";
Put a double backslash instead of a single backslash...
even though this post is quite old I tried something that worked for my case .
I wanted to create a string variable with the value below:
21541_12_1_13\":null
so my approach was like that:
build the string using verbatim
string substring = #"21541_12_1_13\"":null";
and then remove the unwanted backslashes using Remove function
string newsubstring = substring.Remove(13, 1);
Hope that helps.
Cheers
What is the difference between the \ and the / when doing streamwriter?
e.g.
Example 1:
Streamwriter sw = new Streamwriter("/test folder/Output/test.txt");
and
Example 2:
Streamwriter sw = new Streamwriter(#"\test folder\Output\test.txt");
I see you need the # symbol in the front on the second example too.
There is no difference because .NET recognizes both one and the other in paths.
However, since \ has special meaning when appearing inside a string literal (it is the beginning of an escape sequence) the second example uses verbatim string literal syntax. It could have used \\ in place of \ instead.
Adding # only improves readability, a string starting with # will simply have all its \'s replaced by \\ during compile time and \ added where needed.
Both are valid path separator characters in .NET.
IOW, it is exactly the same thing.
The \ is generally used in Windows to separate directories, however I think it does accept / in most circumstances as well.
The \ also needs to be escaped, hence the # symbol. You could also use \\ to escape this character as well.
Because with \ start escape characters. For example "\"" will print ". If you want to use \ as a character either you need to add # in front of string or use \\. As you see it has nothing to do with path-s both form are valid for streamwriter.
So in microsoft visual studio I have a string that is compiled into a regex. My string is "#(\d+(.\d+)?)=(\d+(.\d+)?)". I cannot compile my program because I get an error saying that \d is a unrecognized escape character. How do I tell it to shut up and let me regex like a pro?
Begin your string with #, that causes the compiler to leave (almost) all characters alone, unescaped (the exception is ", which can be escaped as ""):
#"#(\d+(.\d+)?)=(\d+(.\d+)?"
The problem is that c# does not like the \d inside the string. Use a verbatim string instead
string pattern = #"#(\d+(.\d+)?)=(\d+(.\d+)?)";
The "#" denotes it. C# will not look for escape sequences in the string. If you have to escape a " use two "".
Of cause you can use normal strings. but then you will have to escape the backslashes
string pattern = "#(\\d+(.\\d+)?)=(\\d+(.\\d+)?)";
If you're using a normal string, you need to escape your backslashes, like so:
"#(\\d+(.\\d+)?)=(\\d+(.\\d+)?)"
Basically, you're putting a literal string into C#; the C# compiler sees the string first, and tries to interpret \d as an escape sequence (which doesn't exist, hence error). Therefore, you use \\d to get the C# compiler to see the string as \d, which then gets passed to the regex engine (which does recognize \d as something meaningful). (yes, if you want to match a literal backslash in your regex pattern, you need to use \\\\)
But in C#, you have the alternative of just prepending the string with # to get the compiler to leave the string alone (though " still needs escaping), so that would be like this:
#"#(\d+(.\d+)?)=(\d+(.\d+)?)"
You could also use a verbatim string literal (I prefer to use these because of readability).
Use #"(#\d+(.\d+)?)=(\d+(.\d+)?)"
The #" sign indicates that the string shouldn't interpret escaped characters (A character prefixed by a \) until the closing " is reached.
Note: You can match a single " in your search pattern by double quoting instead "". For instance you can match "Hello" by using the pattern #"""\w+"""
I have stringBuilder & string class, storing a path:
StringBuilder name = new StringBuilder();
name.Append(#"NETWORK\MyComputer");
String serverName = name.ToString(); //this converts the \ to a \\
I have tried a number of things, but it always results in the string having \
Using serverName.Replace("\\", #"\"); doesn't work, it leaves it as a \
servername.Replace("\\", "\""); adds a " to the string, which is still not correct.
Please assist.
If you are concerned at a single back slash being shown as a double back slash then don't be - that is simply the way it is shown to you in the debugger.
The back slash is a special character, that 'specialness' is turned off by doubling it up. Alternatively the # symbol can be prefixed to the string in source code which avoids having to use it.
Use
name.Append(Path.Combine("NETWORK", "MyComputer");
In strings \ is an escape sequence. So \ in debugger will be \\
Acc.to MSDN
Character combinations consisting of a backslash (\) followed by a letter or by a combination of digits are called "escape sequences." To represent a newline character, single quotation mark, or certain other characters in a character constant, you must use escape sequences. An escape sequence is regarded as a single character and is therefore valid as a character constant.
Escape sequences are typically used to specify actions such as carriage returns and tab movements on terminals and printers. They are also used to provide literal representations of nonprinting characters and characters that usually have special meanings, such as the double quotation mark ("). The following table lists the ANSI escape sequences and what they represent.
Read Escape Sequences
I don't think your code can be compiled. Because \ is an escape character, thus the string "\" will be wrong. The #"\" is right because the # (literal) has ignored that escape and tread it as a normal character.
See more here
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Possible Duplicate:
What's the # in front of a string for .NET?
I have the following code:
new Attachment(Request.PhysicalApplicationPath + #"pdf\" + pdfItem.Value)
What does the # sign do?
It has nothing to do with filepath. It changes the escaping behavior of strings.
In a string literal prefixed with # the escape sequences starting with \ are disabled. This is convenient for filepaths since \ is the path separator and you don't want it to start an escape sequence.
In a normal string you would have to escape \ into \\ so your example would look like this "pdf\\". But since it's prefixed with # the only character that needs escaping is " (which is escaped as "") and the \ can simply appear.
This feature is convenient for strings literals containing \ such as filepaths or regexes.
For your simple example the gain isn't that big, but image you have a full path "C:\\ABC\\CDE\\DEF" then #"C:\ABC\CDE\DEF" looks a lot nicer.
For regular expressions it's almost a must. A regex typically contains several \ escaping other characters already and often becomes almost unreadable if you need to escape them.
It's a verbatim string literal.
This allows the string to contain backslashes and even linebreaks without them being handled differently:
string multiLineString = #"First line
second line
third line";
As backslashes aren't used for escaping, inserting a double quote into the string requires it to be doubled:
string withQuote = #"before""after";
Verbatim string literals are typically used for file paths (as you've shown) and regular expressions, both of which frequently use backslashes.
See my article on strings for more information.
It allows you to enter the backslash (\) without escaping it:
var s1 = "C:\\Temp\\MyFileName";
var s2 = #"C:\Temp\MyFileName";
Both result in a string with the same contents (and since strings are interned at compile time, probably even the same string reference).