Temporary files

Create a temporary file

TemporaryFile.Create creates an empty file and returns a TemporaryFile that deletes it when disposed. It has three overloads:

// Generated name under the system temp folder
using var temporaryFile = TemporaryFile.Create();
File.WriteAllText(temporaryFile.FullPath, "content");

// Choose the file name; a unique parent folder is created for it
using var namedFile = TemporaryFile.Create("custom.txt");

// Choose the full path. The file must not already exist.
using var atPath = TemporaryFile.Create(FullPath.Combine(Path.GetTempPath(), $"custom-{Guid.NewGuid():N}.txt"));

• The generated names contain the UTC date and time and a GUID, so they are unique.
• A relative path can contain folders, such as data/input.csv: they are created in the unique folder, and deleted with it.
• On Linux and macOS, only the current user can read and write the file.

Choose the file name

Tools often expect a given file name or extension. Pass the name: the file is created in a folder of its own, so the name cannot collide with another file, and that folder is deleted with the file:

FullPath filePath;
using (var file = TemporaryFile.Create("report.csv"))
{
    filePath = file.FullPath;

    // The file exists and is empty; a unique folder holds it, so the name can be chosen freely
    Assert.Equal("report.csv", file.FullPath.Name);
    Assert.Equal(0, new FileInfo(file).Length);

    File.WriteAllText(file, "id,name");
}

// Disposing the instance deletes the file and the folder created for it
Assert.False(File.Exists(filePath));
Assert.False(Directory.Exists(filePath.Parent));

TemporaryFile converts implicitly to string, to FullPath and to FileInfo, so the instance itself can be passed to File.WriteAllText or to any API that takes a path.

Create the file at a given path

Pass a full path to create the file exactly there. The file must not exist yet: an existing file is never adopted, so disposing the instance cannot delete data it did not create:

// Create the file at a path of your choice. The file must not exist yet.
FullPath path = FullPath.GetTempPath() / $"output-{Guid.NewGuid():N}.json";
using (var file = TemporaryFile.Create(path))
{
    Assert.True(File.Exists(path));
    Assert.Throws<IOException>(() => TemporaryFile.Create(path));
}

Assert.False(File.Exists(path));

• An existing file throws an IOException, an empty path or file name an ArgumentException.
• The missing parent folders are created. Disposal deletes the file only, not those folders.

Several files

When you need several files, or files whose names you do not control, use a temporary directory: every file in it is deleted with it.

To create a file with a unique name that you delete yourself, use FullPath.CreateTempFile: see Create a temporary file.