C#: How would you make a unique filename by adding a number?

Question

I would like to create a method which takes either a filename as a string or a FileInfo and adds an incremented number to the filename if the file

Answer 1

This is an answer to question in this Link, but they marked it as a duplicate, so I post my answer here.

I created this proof of concept class (may contain bugs). More explanation in code comments.

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text.RegularExpressions;

namespace ConsoleApp
{
    class Program
    {
        static void Main( string[] args )
        {
            var testFilePaths = new List<string>
            {
                @"c:\test\file.txt",
                @"c:\test\file(1).txt",
                @"c:\test\file(2).txt",
                @"c:\TEST2\file(3).txt",
                @"c:\test\file(5).txt",
                @"c:\test\file(5)abc.txt",
                @"c:\test\file(5).avi"
            };

            // inspect in debbuger for correct values
            var withSuffix      = new DecomposedFilePath( "c:\\files\\file(13).txt");
            var withoutSuffix   = new DecomposedFilePath( "c:\\files\\file(abc).txt");
            var withExtraNumber = new DecomposedFilePath( "c:\\files\\file(34)xyz(35).txt"); // "(34)" in the middle should be ignored

            DecomposedFilePath changedSuffix = withExtraNumber.ReplaceSuffix( 1999 ); // "file(34)xyz(35).txt" -> "file(34)xyz(1999).txt"
            DecomposedFilePath removedSuffix = changedSuffix.ReplaceSuffix( null ); // "file(34)xyz(1999).txt" -> "file(34)xyz.txt"

            var testPath = new DecomposedFilePath( "c:\\test\\file.txt");
            DecomposedFilePath nextPath1 = testPath.GetFirstFreeFilePath( testFilePaths );

            // update our list
            testFilePaths.Add( nextPath1.FullFilePath );
            DecomposedFilePath nextPath2 = testPath.GetFirstFreeFilePath( testFilePaths );
        
            testFilePaths.Add( nextPath2.FullFilePath );
            DecomposedFilePath nextPath3 = testPath.GetFirstFreeFilePath( testFilePaths );
        }
    }

    public sealed class DecomposedFilePath
    {
        public DecomposedFilePath( string filePath )
        {
            FullFilePath = Path.GetFullPath( filePath );
        }

        // "c:\myfiles\file(4).txt"
        public string FullFilePath { get; }

        // "file" or "file(1)"
        public string FileNameWithoutExt => Path.GetFileNameWithoutExtension( FullFilePath );

        // "file(13)" -> "file"
        public string FileNameWithoutExtAndSuffix => FileNameWithoutExt.Substring( 0, FileNameWithoutExt.Length - Suffix.Length ); // removes suffix

        // ".txt"
        public string Extenstion => Path.GetExtension( FullFilePath );

        // "c:\myfiles"
        public string DirectoryPath => Path.GetDirectoryName( FullFilePath );

        // "file(23)" -> "23", file -> stirng.Empty
        public string Suffix
        {
            get
            {
                // we want to extract suffix from file name, e.g. "(34)" from "file(34)"
                // I am not good at regex, but I hope it will work correctly

                var regex = new Regex( @"\([0-9]+\)$" );
                Match match = regex.Match( FileNameWithoutExt );

                if (!match.Success) return string.Empty; // suffix not found

                return match.Value; // return "(number)"
            }
        }

        // tranlates suffix "(33)" to 33. If suffix is does not exist (string.empty), returns null (int?)
        public int? SuffixAsInt
        {
            get
            {
                if (Suffix == string.Empty) return null;

                string numberOnly = Suffix.Substring( 1, Suffix.Length - 2 ); // remove '(' from beginning and ')' from end

                return int.Parse( numberOnly );
            }
        }

        // e.g. input is suffix: 56 then it changes file name from "file(34)" to "file(56)"
        public DecomposedFilePath ReplaceSuffix( int? suffix ) // null - removes suffix
        {
            string strSuffix = suffix is null ? string.Empty : $"({suffix})"; // add ( and )

            string path = Path.Combine( DirectoryPath, FileNameWithoutExtAndSuffix + strSuffix + Extenstion ); // build full path

            return new DecomposedFilePath( path );
        }

        public DecomposedFilePath GetFirstFreeFilePath( IEnumerable<string> filesInDir )
        {
            var decomposed = filesInDir
                // convert all paths to our class
                .Select( x => new DecomposedFilePath( x ) )
                // pick files only with the same extensionm as our base file, ignore case
                .Where( x => string.Equals( Extenstion, x.Extenstion, StringComparison.OrdinalIgnoreCase) )
                // pick files only with the same name (ignoring suffix)
                .Where( x => string.Equals( FileNameWithoutExtAndSuffix, x.FileNameWithoutExtAndSuffix, StringComparison.OrdinalIgnoreCase) )
                // with the same directory
                .Where( x => string.Equals( DirectoryPath, x.DirectoryPath, StringComparison.OrdinalIgnoreCase) )
                .ToList(); // create copy for easier debugging

            if (decomposed.Count == 0) return this; // no name collision

            int? firstFreeSuffix = Enumerable.Range( 1, int.MaxValue) // start numbering duplicates from 1
                                  .Select( x => (int?) x) // change to int? because SuffixAsInt is of that type
                                  .Except( decomposed.Select( x => x.SuffixAsInt) ) // remove existing suffixes
                                  .First(); // get first free suffix

            return ReplaceSuffix( firstFreeSuffix );
        }

        public override string ToString() => FullFilePath;
    }
}

Answer 2

Hope this self iterating function may help. It works fine for me.

public string getUniqueFileName(int i, string filepath, string filename)
    {
        string path = Path.Combine(filepath, filename);
        if (System.IO.File.Exists(path))
        {
            string name = Path.GetFileNameWithoutExtension(filename);
            string ext = Path.GetExtension(filename);
            i++;
            filename = getUniqueFileName(i, filepath, name + "_" + i + ext);
        }
        return filename; 
    }

Answer 3

Lots of good advice here. I ended up using a method written by Marc in an answer to a different question. Reformatted it a tiny bit and added another method to make it a bit easier to use "from the outside". Here is the result:

private static string numberPattern = " ({0})";

public static string NextAvailableFilename(string path)
{
    // Short-cut if already available
    if (!File.Exists(path))
        return path;

    // If path has extension then insert the number pattern just before the extension and return next filename
    if (Path.HasExtension(path))
        return GetNextFilename(path.Insert(path.LastIndexOf(Path.GetExtension(path)), numberPattern));

    // Otherwise just append the pattern to the path and return next filename
    return GetNextFilename(path + numberPattern);
}

private static string GetNextFilename(string pattern)
{
    string tmp = string.Format(pattern, 1);
    if (tmp == pattern)
        throw new ArgumentException("The pattern must include an index place-holder", "pattern");

    if (!File.Exists(tmp))
        return tmp; // short-circuit if no matches

    int min = 1, max = 2; // min is inclusive, max is exclusive/untested

    while (File.Exists(string.Format(pattern, max)))
    {
        min = max;
        max *= 2;
    }

    while (max != min + 1)
    {
        int pivot = (max + min) / 2;
        if (File.Exists(string.Format(pattern, pivot)))
            min = pivot;
        else
            max = pivot;
    }

    return string.Format(pattern, max);
}

Only partially tested it so far, but will update if I find any bugs with it. (Marcs code works nicely!) If you find any problems with it, please comment or edit or something :)

Answer 4

Here's one that decouples the numbered naming question from the check of the filesystem:

/// <summary>
/// Finds the next unused unique (numbered) filename.
/// </summary>
/// <param name="fileName">Name of the file.</param>
/// <param name="inUse">Function that will determine if the name is already in use</param>
/// <returns>The original filename if it wasn't already used, or the filename with " (n)"
/// added to the name if the original filename is already in use.</returns>
private static string NextUniqueFilename(string fileName, Func<string, bool> inUse)
{
    if (!inUse(fileName))
    {
        // this filename has not been seen before, return it unmodified
        return fileName;
    }
    // this filename is already in use, add " (n)" to the end
    var name = Path.GetFileNameWithoutExtension(fileName);
    var extension = Path.GetExtension(fileName);
    if (name == null)
    {
        throw new Exception("File name without extension returned null.");
    }
    const int max = 9999;
    for (var i = 1; i < max; i++)
    {
        var nextUniqueFilename = string.Format("{0} ({1}){2}", name, i, extension);
        if (!inUse(nextUniqueFilename))
        {
            return nextUniqueFilename;
        }
    }
    throw new Exception(string.Format("Too many files by this name. Limit: {0}", max));
}

And here's how you might call it if you are using the filesystem

var safeName = NextUniqueFilename(filename, f => File.Exists(Path.Combine(folder, f)));

Answer 5

/// <summary>
/// Create a unique filename for the given filename
/// </summary>
/// <param name="filename">A full filename, e.g., C:\temp\myfile.tmp</param>
/// <returns>A filename like C:\temp\myfile633822247336197902.tmp</returns>
public string GetUniqueFilename(string filename)
{
    string basename = Path.Combine(Path.GetDirectoryName(filename),
                                   Path.GetFileNameWithoutExtension(filename));
    string uniquefilename = string.Format("{0}{1}{2}",
                                            basename,
                                            DateTime.Now.Ticks,
                                            Path.GetExtension(filename));
    // Thread.Sleep(1); // To really prevent collisions, but usually not needed
    return uniquefilename;
}

As DateTime.Ticks has a resolution of 100 nanoseconds, collisions are extremely unlikely. However, a Thread.Sleep(1) will ensure that, but I doubt that it's needed

Answer 6

public FileInfo MakeUnique(string path)
{            
    string dir = Path.GetDirectoryName(path);
    string fileName = Path.GetFileNameWithoutExtension(path);
    string fileExt = Path.GetExtension(path);

    for (int i = 1; ;++i) {
        if (!File.Exists(path))
            return new FileInfo(path);

        path = Path.Combine(dir, fileName + " " + i + fileExt);
    }
}

Obviously, this is vulnerable to race conditions as noted in other answers.