Question

I need to validate a folder name in c#.

I have tried the following regex :

 ^(.*?/|.*?\\)?([^\./|^\.\\]+)(?:\.([^\\]*)|)$

but it fails and I also tried using GetInvalidPathChars().

It fails when i try using P:\abc as a folder name i.e Driveletter:\foldername

Can anyone suggest why?

Answer 1

You could do that in this way (using System.IO.Path.InvalidPathChars constant):

bool IsValidFilename(string testName)
{
    Regex containsABadCharacter = new Regex("[" + Regex.Escape(System.IO.Path.InvalidPathChars) + "]");
    if (containsABadCharacter.IsMatch(testName) { return false; };

    // other checks for UNC, drive-path format, etc

    return true;
}

[edit]
If you want a regular expression that validates a folder path, then you could use this one:

Regex regex = new Regex("^([a-zA-Z]:)?(\\\\[^<>:\"/\\\\|?*]+)+\\\\?$");

[edit 2]
I’ve remembered one tricky thing that lets you check if the path is correct:

var invalidPathChars = Path.GetInvalidPathChars(path)

or (for files):

var invalidFileNameChars = Path.GetInvalidFileNameChars(fileName)