How do I check if a given string is a legal/valid file name under Windows?

Question

I want to include a batch file rename functionality in my application. A user can type a destination filename pattern and (after replacing some wildcards in the pattern) I n

Answer 1

For .Net Frameworks prior to 3.5 this should work:

Regular expression matching should get you some of the way. Here's a snippet using the 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;
}

For .Net Frameworks after 3.0 this should work:

http://msdn.microsoft.com/en-us/library/system.io.path.getinvalidpathchars(v=vs.90).aspx

Regular expression matching should get you some of the way. Here's a snippet using the System.IO.Path.GetInvalidPathChars() constant;

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

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

    return true;
}

Once you know that, you should also check for different formats, eg c:\my\drive and \\server\share\dir\file.ext