Process a file as a lazy line sequence.

C#: ReadLines avoids allocating one string containing the entire file.

using System;
using System.IO;
using System.Linq;
using System.Text;
using System.Text.Json;
using System.Text.RegularExpressions;
using System.Collections.Generic;
using System.Globalization;
using System.Security.Cryptography;
using System.Threading;
using System.Threading.Tasks;

foreach (string line in File.ReadLines("lines.txt", Encoding.UTF8))
    Console.WriteLine(line.ToUpperInvariant());

Expected output EXAMPLE

ONE
TWO

Details

Use Program.cs in a .NET 8 console project and run dotnet run. Uses only the .NET standard libraries. ReadLines avoids allocating one string containing the entire file.

✓ Verified

Tested on Ubuntu 24.04.5 LTS · 2026-11-02 18:05:57 UTC · 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: 94c08d803bba18049e233148f6556faf693b2364019e4ce2baeea1d5bcfee60b
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 'one\ntwo\n' > lines.txt

Observed standard output

ONE
TWO

Exit code: 0. Standard error: empty. Validation: Exact stdout comparison. System-dependent values above are one recorded run.