Append a line.
Append UTF-8 text without replacing existing C# file contents.
using System;
using System.IO;
using System.Linq;
using System.Collections.Generic;
using System.Text.Json;
File.AppendAllText("notes.txt", "second\n");
Console.Write(File.ReadAllText("notes.txt"));Expected output EXAMPLE
first second
Details
Use Program.cs in a .NET 8 console project (dotnet new console --framework net8.0), then dotnet run. Uses only the .NET standard libraries.
Tested on Ubuntu 24.04.5 LTS · · 8.0.425 · libc6 2.39-0ubuntu8.9
Test inputs, results and environment
The exact published code ran in a dedicated Linux test container with prepared inputs. Unprivileged snippet process, external networking disabled, read-only root filesystem, and a fresh temporary working directory. Fixtures and output records are isolated from the application database. Testing covers this example and its stated checks, not every input, operating system, or runtime version. The Linux container shares its host's kernel; this is not a native Windows test.
- Architecture / host kernel
- x86_64 / 6.18.54.1-microsoft-standard-WSL2
- Snippet identity / locale
- uid=65534, gid=65534 (unprivileged) / C.UTF-8
- Interpreter invocation
dotnet build --no-restore && dotnet out/csharp.dll- Container image ID
sha256:32dc2d998158b6554c99b73b533f423696a0f3e31e8cbea9db10b5eee9a2fadd- Code SHA-256
e3800b7dcc9898e883146c4e5e7c93c922fdae329aac1821bff9768a02cea6b2- Dependencies
- libc6 2.39-0ubuntu8.9
Test input setup
These are the prepared inputs used by the test harness. See Details above for the prerequisites and how to run this example.
printf 'first\n' > notes.txt
Observed standard output
first second
Exit code: 0. Standard error: empty. Validation: Exact stdout comparison. System-dependent values above are one recorded run.