Get list of files in directory with exclude option

Question

This method returns the list of files (absolute path) in a folder (or tree). It allows filtering by extensions or filenames.

The method receives the following parameters:

• string path: folder path to scan for files.
• string[] exclude: can contain filenames such as "read.me" or extensions such as "*.jpg".
• SearchOption searchOption: TopDirectoryOnly to scan only the specified folder or AllDirectories to scan tree folder under the specified path.

The method return files that doesn't appear in exclude array and a) hasn't extension, or b) extension doesn't appear in exclude array.

---

    public static IEnumerable<string> GetFiles(string path, string[] exclude, SearchOption searchOption = SearchOption.AllDirectories)
    {
        IEnumerable<string> files = Directory.EnumerateFiles(path, "*.*", searchOption);
        var resultFiles = new List<string>();

        if (exclude.Length > 0)
        {
            foreach (var filename in files)
            {
                string extension = Path.GetExtension(filename);

                if (Array.IndexOf(exclude, Path.GetFileName(filename)) >= 0)
                {
                    continue;
                }

                if (string.IsNullOrEmpty(extension) || Array.IndexOf(exclude, "*" + extension) < 0)
                {
                    resultFiles.Add(filename);
                }
            }
        }

        return resultFiles;
    }

Answer 1

You're already returning an IEnumerable<T> so you might as well turn it into an iterator block. Discard the local resultFiles and simply use yield return filename.

MSDN on yield

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I don't like that both filenames and extensions are in the same array. If you have 1 extension and 5000 files that have to be excluded, it will iterate over 5000 files (if you have bad luck) for no reason.

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I would consider using the .Contains() extension method: it's just more expressive than Array.IndexOf and should be no difference in performance.

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I prefer string.IsNullOrWhiteSpace since that also takes care of.. well.. whitespace. You never know if the pesky QA departement tries something like that.

---

IEnumerable<string> files = Directory.EnumerateFiles(path, "*.*", searchOption);

if (exclude.Length > 0)
{
}

return resultFiles;

If there is nothing to exclude, you won't include anything either.

---

A new implementation might look like this:

public static IEnumerable<string> GetFiles(string path, IEnumerable<string> excludedFiles, IEnumerable<string> excludedExtensions, SearchOption searchOption = SearchOption.AllDirectories)
{
    var files = Directory.EnumerateFiles(path, "*.*", searchOption);

    foreach(var file in files)
    {
        if(excludedFiles.Contains(file))
        {
            continue;
        }

        if(excludedExtensions.Contains(Path.GetExtension(file)))
        {
            continue;
        }

        yield return file;
    }
}

Answer 2

A few things I noticed:

• If the exclude array is empty you return an empty list instead of every file.

• reversing your logic would allow you to check everything in one statement.

• Since you're returning an IEnumerable<string> already, using the yield operator would make sense here.

• Accepting an IEnumerable<string> instead of an string[] for the exclude parameter, gives the user more options. Also this allows you to leverage the LINQ extensions better.

Your code could look something like this:

public static IEnumerable<string> GetFiles(string path, IEnumerable<string> exclude, SearchOption searchOption = SearchOption.AllDirectories)
{
    IEnumerable<FileInfo> files = new DirectoryInfo(path).EnumerateFiles("*.*", searchOption);
    foreach (var filename in files)
    {

        if (!exclude.Any(x => x == filename.Name || (x.StartsWith("*") && x.Contains(filename.Extension))))
        {
            yield return filename.Name;
        }

    }
}

Answer 3

The most important thing is that your code does not do lazy enumeration, which means it will load every filenames in your whole drive into memory if you use this method on root directory. To avoid that, the method should either return filtered IEnumerable<string> from LINQ method or using yield return. Using LINQ is more convenient:

private static bool IsExcluded(string fileName, string[] exclude) {
    // if not excluded by filename
    if (exclude.Contains(Path.GetFileName(fileName))) return true;
    string extension = Path.GetExtension(fileName);
    return extension == null || exclude.Contains("*" + extension);
}

public static IEnumerable<string> GetFiles(string path, 
    string[] exclude = null, 
    SearchOption searchOption = SearchOption.AllDirectories)
{
    // I prefer using var keyword for any IEnumerable
    var files = Directory.EnumerateFiles(path, "*.*", searchOption);
    if (exclude != null && exclude.Length > 0) {
        files = files.Where(f => !IsExcluded(f, exclude));
    }
    return files;
}

I separate exclusion checking into a new method because it is easier to verify that the filter work correctly rather than doing it inline.

Answer 4

Everything that you have written there can be done with a call to: Directory.GetFiles(string, string, SearchOption)