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What can be the regular expression or regex for a file path or path?

I am new to this. Please can anyone tell me what can be the regular expression for file path or any path :
Ex => "C:\\\\Users\\\\1700000\\\\Downloads\\\\BackendApp\\\\WebApplication\\\\WebAPI_APPL\\\\Data\\\\1\\\\FirstFol\\\\SecondFodler\\\\MainFolder\\\\File.xlsx"
or
"C:\\\\Users\\\\1700000\\\\Downloads\\\\BackendApp\\\\WebApplication\\\\WebAPI_APPL\\\\Data\\\\1\\\\FirstFol\\\\SecondFodler\\\\MainFolder"
File path or path can be small or big, it is not fixed. Path should start with "C(any drive):\\"
Please let me know what can I use also the expression should consider double backslash in it.
This expressions didn't work
#"^(?:[\w]\:|\\\\)(\\\\[a-z_\-\s0-9\.]+)+\.(txt|gif|pdf|doc|docx|xls|xlsx)$"
#"^(?:[a-zA-Z]\:|\\\\\\\\[\w\.]+\\\\[\w.$]+)\\\\(?:[\w]+\\\\)*\w([\w.])+$"

Here's one i've used in the past for unix based systems
(\/)((\w|-|_|[0-9])*\/(\w|-|_|[0-9])*)+[^.*\.]
For windows it will be essentially the same + detecting drive letter :
([A-Z]{1}:)(\/)((\w|-|_|[0-9])*\/(\w|-|_|[0-9])*)+[^.*\.]*
With backslashes :
([A-Z]{1}:)(\\\\)((\w|-|_|[0-9])*\\\\(\w|-|_|[0-9])*)+[^.*\.]*
When I used it I expected my strings to be paths only. It may capture text after a path so it's not perfect. But I hope this helps.

Try this one:
^(?:[\w]:|\\)([A-Za-z_\s0-9.-\\]+)\.(txt|gif|pdf|docx|doc|xlsx|xls)$
you could use https://regex101.com/ to try yours regex

Spaces in file path

I'm creating a console application in C#, and I want to check if a specific file (foo.exe). But when the path contains spaces (C:\A Folder With Spaces\) it checks if foo.exe exists at this directory: C:\A.
Question: How can I check inside of a folder that contains spaces?

It looks like you are passing the name of the file as command-line parameter. In this case the split at the space is done by Windows cmd command processor when you pass C:\A Folder With Spaces\ as parameter. To fix this, enclose the file name in doublequotes:
c:\test>myprog.exe "C:\A Folder With Spaces\foo.exe"

If (File.Exists(#"C:\A Folder With Spaces\foo.exe")
{
//the # sign makes the spaces be taken literally.
}

Sounds like you're supplying the path as an argument to the console application? In which case enclose the path argument in quotes

System.ArgumentException: Illegal characters in path. error

I`m getting an ArgumentException from the following code:
string strPath="C:\somename.xls";
startPath=System.IO.Path.GetDirectoryName(System.Diagnostics.Process.GetCurrentProcess().MainModule.FileName);
filePath = System.IO.Path.Combine(startPath, strPath);
I found this code on Stack Overflow.
Link:
C#:Copy protected worksheet to another excel file
I don't exactly know what it is. Please tell me what it is. This code I'm building into an exe.
Lastly, I need to Copy one worksheet to another file.
What`s wrong am I doing? I deploy this in server.

what that code appears to do, is it gets your working directory(wherever the exe associated with your code is), and combines it with "C:\\somename.xls"(which doesn't make sense.)
I think you might have intended something like
string strPath=#"somename.xls";
so assume you're running your application from
"C:\Users\owner\documents\visual studio 2012\Projects\ConsoleApplication1\ConsoleApplication1\bin\Debug"
what that code would do is set filePath to
"C:\Users\owner\documents\visual studio 2012\Projects\ConsoleApplication1\ConsoleApplication1\bin\Debug\somename.xls"
the first thing I saw was
string filePath="C:\somename.xls";
\ is a special character, for determining other characters. for instance '\n' is a newline. '\\' is the actual backslash.
so, you want to escape your \ with another \
string filePath="C:\\somename.xls";
or make it a literal string by putting a # in front of it.
string filePath=#"C:\somename.xls";

Your code should be:
string filePath = "C:\\somename.xls"
You need double backslashes.

Two problems with the code,
First
string filePath="C:\somename.xls";
\ is a special character, for determining other characters. for instance '\n' is a newline. '\\' is the actual backslash.
Second
filePath contains a root path, C:\\. Path.Combine will just return filePath then, it cannot be combined.

Your main problem is in startPath parameter.
System.Diagnostics.Process.GetCurrentProcess().MainModule.FileName
If you trace your code, in FileName you will see a bad symbol character witch is illegal

Escaping directory chars in C#

I need to escape chars in a string I have, which content is C:\\blablabla\blabla\\bla\\SQL.exe to C:\blablabla\blabla\bla\SQL.exe so I could throw a process based on this SQL.exe file.
I tried with Mystring.Replace("\\", #"\"); and Mystring.Replace(#"\\", #"\"); but none worked.
How could I do this?
EDITED: Corrected type in string.

I very strongly suspect that you are looking this input string in the Visual Studio debugger and fooling yourself that there are actually 2 \ whereas in reality there aren't. That's the reason why attempting to replace \\ with \ doesn't do anything because in the original string there is no occurrence of \\. And since you are looking the output once again in the debugger, you are once again fooling yourself that there are 2 \.
Visual Studio debugger has this tendency to escape strings. Log it to a file or print to the console and you will see that there is a single \ in your input string and you don't need to replace anything.

It looks like you're trying to replace double backslash (#"\\") in a string with single backslash (#"\"). If so try the following
Mystring = Mystring.Replace(#"\\", #"\");
Note: Are you sure that the string even contains double backslashes? Certain environments will print out a single backslash as a double (debugger for example). Your comment mentioned my approach didn't work. That's a flag that there's not actually a double backslash in your string (else it would work).

The # character specifies a string as a verbatim literal string, but that is when constructing a string. If you use Mystring.Replace("\\", #"\") then nothing will be replaced, essentially, as the two strings are the same.
If you want a string without the escape characters, then either define it with:
string path = #"C:\Some\Directory\And\File.txt";
Or you can replace the \\ with / like so:
path = path.Replace('\\', '/');
It is worth noting, as mentioned by Darin Dimitrov, that the string containing two \ characters is likely just the display of the string (i.e. when using the debugger) and not the actual value of the string.

i think OP is asking how to escape \\ in File Path, if that in the case, as OP is not mentioning where he's trying to use this. so i'm putting a guess.
Then You use Path.Combine() method to get the FileName path.
Path.Combine() Documentation

where are you looking at this output? because it could be the string is what you expect, but viewing the value through the debugger, output window, etc. is escaping the slash

Use something like:
myStr = myStr.Replace(#"\\", #"\");
Make sure you assign the result of Replace method to myStr. Otherwise it goes into void ;)

Try adding "|DataDirectory|\MyFile.xyz" where you need it. It works with connection strings it might work with something else (I haven't really tried to apply it to something else).

I didn't understand what you want, if you just want do get the file name (escape directory chars) you can try:
string fileName = Path.GetFileName(YourString)

Noloman.... when you concatenate are you perhaps missing a "\" when concatenating the directory.. I am assuming that you are trying to join directory + some sub directory.. #noloman keep in mind that in C# "c:\Temp" is written like this "c:\Temp" or #"c:\Temp" one is Literal the other is how to represent a "\" in the legacy way of coding because the "\" is an escape Char and when dealing with directorys we represent all paths and sub paths with "\"
so perhaps by you replacing the "\" you are truly messing up your own expected process
Mystring = Mystring.Replace(#"\\", #"\");
should work for you unless you are truly meaning to do
Mystring = Mystring.Replace(#"\", "\"); which if you believe that you are expecting a "\" to be used to build the directory.. then of course it will not work.. because you have just in essense replaced the backslash with a return char.. I hope that this makes sense to you..
System.IO.Directory.GetCurrentDirectory(); you are using is also an Issue.. SQL Server is not that application thats running the code.. it's your .NET application so you need to either put the location of the SQL Server into a variable, app.config, web.config ect... please edit your question and paste the code that you are using to do what it is that you want to do inregards to the SQL Server Code.. you would probably want to look at the Are you wanting to do something like Process.Start(....) meaning the file name..?

How to return a verbatim string from ConfigurationManager.AppSetting["settingname"].ToString()

I am using the ConfigurationManager.AppSetting["blah"].ToString() method to get the path to the folder that contains the files I'm needing. But I'm throwing an UnsupportedFormatException on the path when it tries to use Directory.GetFiles(path).
The returning value has the escape characters included and I'm not sure how to keep it from returning the extra characters. This is what the path looks like after it is returned:
\\\\\\\\C:\\\\folder1\\\\folder2

I needed to remove the first four "\" to give it a correct path.

you have extra back-slash \ at the beginning of your path.
try putting "C:\folder1\folder2" instead of "\\C:\folder1\folder2" in your config file, and it will work.