Find duplicate lines in a file and count how many time each line was duplicated

Updated NOTE on this solution: Checking with FileAccess.ReadWrite will fail for Read-Only files so the solution has been modified to check with FileAccess.Read.

ORIGINAL: I've used this code for the past several years, and I haven't had any issues with it.

Understand your hesitation about using exceptions, but you can't avoid them all of the time:

protected virtual bool IsFileLocked(FileInfo file)
{
    try
    {
        using(FileStream stream = file.Open(FileMode.Open, FileAccess.Read, FileShare.None))
        {
            stream.Close();
        }
    }
    catch (IOException)
    {
        //the file is unavailable because it is:
        //still being written to
        //or being processed by another thread
        //or does not exist (has already been processed)
        return true;
    }

    //file is not locked
    return false;
}

Use -o, which means "or":

find Documents \( -name "*.py" -o -name "*.html" \)

You'd need to build that command line programmatically, which isn't that easy.

Are you using bash (or Cygwin on Windows)? If you are, you should be able to do this:

ls **/*.py **/*.html

which might be easier to build programmatically.