How to Rename Files and Folders in C#: .NET 10 update and batch rename fix

files-csharp/RenameFilesWithCSharp/RenameFilesWithCSharp/FileRenameService.cs

@@ -22,4 +22,13 @@ public static void ExecuteRenameFileWithFileClass()
 
         Directory.Delete(directoryPath, true);
     }
-}
+
+    public static string ChangeExtension(string filePath, string newExtension)
+    {
+        var newFilePath = Path.ChangeExtension(filePath, newExtension);
+
+        File.Move(filePath, newFilePath);
+
+        return newFilePath;
+    }
+}

files-csharp/RenameFilesWithCSharp/RenameFilesWithCSharp/FolderRenameService.cs

@@ -0,0 +1,27 @@
+namespace RenameFilesWithCSharp;
+
+public static class FolderRenameService
+{
+    public static void RenameFolder(string oldFolder, string newFolder)
+    {
+        Directory.Move(oldFolder, newFolder);
+    }
+
+    public static void ExecuteRenameFolder()
+    {
+        var parentPath = Path.Combine(Path.GetTempPath(), Path.GetRandomFileName());
+
+        var oldFolder = Path.Combine(parentPath, "Invoices2025");
+        Directory.CreateDirectory(Path.Combine(oldFolder, "Q1"));
+        File.Create(Path.Combine(oldFolder, "Q1", "invoice-001.pdf")).Dispose();
+
+        var newFolder = Path.Combine(parentPath, "Invoices-2025");
+
+        RenameFolder(oldFolder, newFolder);
+
+        Console.WriteLine($"Renamed {Path.GetFileName(oldFolder)} to {Path.GetFileName(newFolder)}");
+        Console.WriteLine($"Invoice moved along: {File.Exists(Path.Combine(newFolder, "Q1", "invoice-001.pdf"))}");
+
+        Directory.Delete(parentPath, true);
+    }
+}

files-csharp/RenameFilesWithCSharp/RenameFilesWithCSharp/ImageRenameService.cs

@@ -16,11 +16,45 @@ public static void RenameImagesWithDateTime(string directoryPath)
 
             var fileExtension = Path.GetExtension(imageFile);
 
-            var newFileName = $"Image_{creationTime:yyyy-MM-dd_HHmmss}{fileExtension}";
+            var baseName = $"Image_{creationTime:yyyy-MM-dd_HHmmss}";
 
-            var newFilePath = Path.Combine(directoryPath, newFileName);
+            var newFilePath = Path.Combine(directoryPath, $"{baseName}{fileExtension}");
+
+            for (var copy = 1; File.Exists(newFilePath) && newFilePath != imageFile; copy++)
+            {
+                newFilePath = Path.Combine(directoryPath, $"{baseName}_{copy}{fileExtension}");
+            }
 
             File.Move(imageFile, newFilePath);
         }
     }
-}
+
+    public static void RenameImagesWithDateTimeUsingFileInfo(string directoryPath)
+    {
+        var allowedExtensions = new[] { ".jpg", ".png", ".jpeg", ".gif" };
+
+        var imageFiles = Directory.EnumerateFiles(directoryPath)
+            .Where(file => allowedExtensions.Contains(Path.GetExtension(file),
+                                StringComparer.OrdinalIgnoreCase));
+
+        foreach (var imageFile in imageFiles)
+        {
+            var file = new FileInfo(imageFile);
+
+            var creationTime = file.CreationTime;
+
+            var fileExtension = file.Extension;
+
+            var baseName = $"Image_{creationTime:yyyy-MM-dd_HHmmss}";
+
+            var newFilePath = Path.Combine(directoryPath, $"{baseName}{fileExtension}");
+
+            for (var copy = 1; File.Exists(newFilePath) && newFilePath != imageFile; copy++)
+            {
+                newFilePath = Path.Combine(directoryPath, $"{baseName}_{copy}{fileExtension}");
+            }
+
+            file.MoveTo(newFilePath);
+        }
+    }
+}

files-csharp/RenameFilesWithCSharp/RenameFilesWithCSharp/Program.cs

@@ -0,0 +1,6 @@
+using RenameFilesWithCSharp;
+
+FileFinderService.ExecuteFindFilesInFolder();
+FileRenameService.ExecuteRenameFileWithFileClass();
+FileInfoRenameService.ExecuteRenameFileWithFileInfoClass();
+FolderRenameService.ExecuteRenameFolder();

files-csharp/RenameFilesWithCSharp/RenameFilesWithCSharp/RenameFilesWithCSharp.csproj

@@ -1,8 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <OutputType>Library</OutputType>
-    <TargetFramework>net8.0</TargetFramework>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net10.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
   </PropertyGroup>
-</Project>
+</Project>

files-csharp/RenameFilesWithCSharp/Tests/RenameFilesUnitTests.cs

@@ -97,4 +97,88 @@ public void WhenBatchRenamingPhotosWithDateTimeAndNoAllowedExtensionsExist_ThenN
         // Assert
         Assert.Equal(existingFiles, updatedFiles);
     }
-}
+
+    [Fact]
+    public void WhenTwoPhotosShareACreationSecond_ThenBothAreRenamedWithoutCollision()
+    {
+        var first = Path.Combine(_tempDirectory, "a.jpg");
+        var second = Path.Combine(_tempDirectory, "b.jpg");
+        File.Create(first).Close();
+        File.Create(second).Close();
+        var sameSecond = new DateTime(2025, 6, 1, 10, 30, 0);
+        File.SetCreationTime(first, sameSecond);
+        File.SetCreationTime(second, sameSecond);
+
+        // Act
+        ImageRenameService.RenameImagesWithDateTime(_tempDirectory);
+
+        // Assert
+        var names = Directory.GetFiles(_tempDirectory).Select(f => Path.GetFileName(f)).Order(StringComparer.Ordinal).ToArray();
+        Assert.Equal(["Image_2025-06-01_103000.jpg", "Image_2025-06-01_103000_1.jpg"], names);
+    }
+
+    [Fact]
+    public void WhenBatchRenameRunsTwice_ThenSecondRunChangesNothing()
+    {
+        var sameSecond = new DateTime(2025, 6, 1, 10, 30, 0);
+        foreach (var name in new[] { "a.jpg", "b.jpg" })
+        {
+            var path = Path.Combine(_tempDirectory, name);
+            File.Create(path).Close();
+            File.SetCreationTime(path, sameSecond);
+        }
+        ImageRenameService.RenameImagesWithDateTimeUsingFileInfo(_tempDirectory);
+        var afterFirstRun = Directory.GetFiles(_tempDirectory).Order().ToArray();
+
+        // Act
+        ImageRenameService.RenameImagesWithDateTimeUsingFileInfo(_tempDirectory);
+
+        // Assert
+        Assert.Equal(afterFirstRun, Directory.GetFiles(_tempDirectory).Order().ToArray());
+    }
+
+    [Fact]
+    public void GivenExistingFolder_WhenRenamingFolder_ThenContentMovesWithIt()
+    {
+        var oldFolder = Path.Combine(_tempDirectory, "Invoices2025");
+        Directory.CreateDirectory(oldFolder);
+        File.WriteAllText(Path.Combine(oldFolder, "invoice-001.pdf"), "content");
+        var newFolder = Path.Combine(_tempDirectory, "Invoices-2025");
+
+        // Act
+        FolderRenameService.RenameFolder(oldFolder, newFolder);
+
+        // Assert
+        Assert.False(Directory.Exists(oldFolder));
+        Assert.True(File.Exists(Path.Combine(newFolder, "invoice-001.pdf")));
+    }
+
+    [Fact]
+    public void GivenTextFile_WhenChangingExtension_ThenOnlyExtensionChanges()
+    {
+        var filePath = Path.Combine(_tempDirectory, "notes.txt");
+        File.WriteAllText(filePath, "content");
+
+        // Act
+        var newFilePath = FileRenameService.ChangeExtension(filePath, ".md");
+
+        // Assert
+        Assert.Equal(Path.Combine(_tempDirectory, "notes.md"), newFilePath);
+        Assert.True(File.Exists(newFilePath));
+        Assert.False(File.Exists(filePath));
+    }
+
+    [Fact]
+    public void GivenExistingDestination_WhenMovingWithoutOverwrite_ThenIOException()
+    {
+        var source = Path.Combine(_tempDirectory, "a.txt");
+        var destination = Path.Combine(_tempDirectory, "b.txt");
+        File.WriteAllText(source, "new");
+        File.WriteAllText(destination, "old");
+
+        Assert.Throws<IOException>(() => File.Move(source, destination));
+
+        File.Move(source, destination, overwrite: true);
+        Assert.Equal("new", File.ReadAllText(destination));
+    }
+}

files-csharp/RenameFilesWithCSharp/Tests/Tests.csproj

@@ -1,24 +1,24 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFramework>net8.0</TargetFramework>
+    <TargetFramework>net10.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
     <IsPackable>false</IsPackable>
     <IsTestProject>true</IsTestProject>
   </PropertyGroup>
   <ItemGroup>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.5.0" />
-    <PackageReference Include="xunit" Version="2.4.2" />
-    <PackageReference Include="xunit.runner.visualstudio" Version="2.4.5">
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.11.0" />
+    <PackageReference Include="xunit" Version="2.9.3" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="4.0.1">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>
     </PackageReference>
-    <PackageReference Include="coverlet.collector" Version="3.2.0">
+    <PackageReference Include="coverlet.collector" Version="10.1.0">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>
     </PackageReference>
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\RenameFilesWithCSharp\RenameFilesWithCSharp.csproj" />
   </ItemGroup>
-</Project>
+</Project>