Regular Expression for validating Windows-based file paths including UNC paths

Question

I wanted to validate a file name along with its full path. I tried certain Regular Expressions as below but none of them worked correctly.

^(?:[\w]\:|\\)(\\[a-z_\-\s0-9\.]+)+\.(txt|gif|pdf|doc|docx|xls|xlsx)$
and
^(([a-zA-Z]\:)|(\\))(\\{1}|((\\{1})[^\\]([^/:*?<>""|]*))+)$
etc...

My requirement is as mentioned below: Lets say if the file name is "c:\Demo.txt" then it should check every possibilites like no double slash should be included(c:\\Demo\\demo.text) no extra colon like(c::\Demo\demo.text). Should accept UNC files like(\\staging\servers) and others validation as well. Please help. I am really stuck here.

not homework actually. Some important work has been stuck bcoz of this. — Running Rabbit, Aug 02 '12 at 12:11
If your file is uploaded then are you really concerned by the path name or only on the filename part? — Steve, Aug 02 '12 at 12:16
File is getting uploaded, as their are no validation applied to it. I just want to provide validation to the file name. Can you help me? — Running Rabbit, Aug 02 '12 at 12:43
possible duplicate of [In C# check that filename is *possibly* valid (not that it exists)](http://stackoverflow.com/questions/422090/in-c-sharp-check-that-filename-is-possibly-valid-not-that-it-exists) — Patrick McDonald, Aug 02 '12 at 14:56
[This question](http://stackoverflow.com/questions/6063418/need-help-with-a-file-path-validation-regular-expression) contains a partial answer. — Allon Guralnek, Aug 02 '12 at 21:46

ykatchou · Answer 1 · 2012-08-02T12:17:50.540

2

Why are you not using the File class ? Always use it !

File f = null;
string sPathToTest = "C:\Test.txt";
try{
f = new File(sPathToTest );
}catch(Exception e){
   Console.WriteLine(string.Format("The file \"{0}\" is not a valid path, Error : {1}.", sPathToTest , e.Message);
}

MSDN : http://msdn.microsoft.com/en-gb/library/system.io.file%28v=vs.80%29.aspx

Maybe you're just looking for File.Exists ( http://msdn.microsoft.com/en-gb/library/system.io.file.exists%28v=vs.80%29.aspx )

Also take a look to the Path class ( http://msdn.microsoft.com/en-us/library/system.io.path.aspx )

The GetAbsolutePath could be one way to get what you want! ( http://msdn.microsoft.com/en-us/library/system.io.path.getfullpath.aspx )

string sPathToTest = "C:\Test.txt";
string sAbsolutePath = "";
try{
   sAbsolutePath = Path.GetAbsolutePath(sPathToTest);
   if(!string.IsNullOrEmpty(sAbsolutePath)){
     Console.WriteLine("Path valid");
   }else{
     Console.WriteLine("Bad path");
   }
}catch(Exception e){
   Console.WriteLine(string.Format("The file \"{0}\" is not a valid path, Error : {1}.", sPathToTest , e.Message);

}

edited Aug 02 '12 at 12:17

answered Aug 02 '12 at 12:11

ykatchou

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I have tried this also. but it was not good in helping. So I thought of going for Regular Expression.. – Running Rabbit Aug 02 '12 at 12:12
The file will be uploaded. the name of the file is coming in request – Running Rabbit Aug 02 '12 at 12:13
It is generally not a good idea to use exception-handling for validating inputs as it incurs significant computational overhead. – Christopher King Dec 30 '13 at 19:31
I agree, but I don't see any other way in this case. Maybe doing a File.Exist if it's a local path (not unc). – ykatchou Dec 31 '13 at 11:09

Steve · Answer 2 · 2012-08-02T12:54:50.060

If you are interested only in the filename part (and not the whole path because you get the file via upload) then you could try something like this:

string uploadedName =  @"XX:\dem<<-***\demo.txt";

int pos = uploadedName.LastIndexOf("\\");
if(pos > -1)
    uploadedName = uploadedName.Substring(pos+1);

var c = Path.GetInvalidFileNameChars();
if(uploadedName.IndexOfAny(c) != -1)
     Console.WriteLine("Invalid name");
else
     Console.WriteLine("Acceptable name");

This will avoid the use of Exceptions as method to drive the logic of your code.

Regular Expression for validating Windows-based file paths including UNC paths

2 Answers2