How to log to a file without using third party logger in .Net Core?

How to log to a file without using third party logger (serilog, elmah etc.) in .NET CORE?

public void ConfigureServices(IServiceCollection services)
{
    services.AddLogging();
}

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
{
    loggerFactory.AddConsole(Configuration.GetSection("Logging"));
    loggerFactory.AddDebug();
}

Issue http://github.com/aspnet/Logging/issues/441 is closed and MS officially recommends to use 3rd party file loggers. You might want to avoid using heavyweight logging frameworks like serilog, nlog etc because they are just excessive in case if all you need is a simple logger that writes to a file and nothing more (without any additional dependencies).

I faced the same situation, and implemented simple (but efficient) file logger: https://github.com/nreco/logging

• can be used in .NET Core 1.x and .NET Core 2.x / 3.x apps
• supports custom log message handler for writing logs in JSON or CSV
• implements simple 'rolling file' feature if max log file size is specified

.NET Core does not (and probably will not) provide a built-in ILoggerProvider implementation for file logging.

There is a facade which makes trace source logging (the built-in logger framework originated in classic .NET) available for .NET Core applications. It can be ok for those who are already familiar with it, but be prepared that configuration is somewhat cumbersome on .NET Core (for details, see this nice article).

As an alternative, you may try my lightweight ILogger<T> implementation which covers the features of the built-in ConsoleLogger and provides additional essential features and good customizability. My library is free, open-source and has only framework dependencies. It completely conforms with the Microsoft provider implementations.

Usage is as simple as follows:

dotnet add package Karambolo.Extensions.Logging.File

ASP.NET Core 3.x web applications:

public static IHostBuilder CreateHostBuilder(string[] args) =>
    Host.CreateDefaultBuilder(args)
        .ConfigureWebHostDefaults(webBuilder =>
        {
            webBuilder
                .ConfigureLogging((ctx, builder) =>
                {
                    builder.AddConfiguration(ctx.Configuration.GetSection("Logging"));
                    builder.AddFile(o => o.RootPath = ctx.HostingEnvironment.ContentRootPath);
                })
                .UseStartup<Startup>();
        });

ASP.NET Core 2.1+ web applications:

public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
    WebHost.CreateDefaultBuilder(args)
        .ConfigureLogging((ctx, builder) =>
        {
            builder.AddConfiguration(ctx.Configuration.GetSection("Logging"));
            builder.AddFile(o => o.RootPath = ctx.HostingEnvironment.ContentRootPath);
        })
        .UseStartup<Startup>();

.NET Core 2.1+ console applications:

// build configuration
// var configuration = ...;

// configure DI
var services = new ServiceCollection();

services.AddLogging(builder =>
{
    builder.AddConfiguration(configuration.GetSection("Logging"));
    builder.AddFile(o => o.RootPath = AppContext.BaseDirectory);
});

// create logger factory
using (var sp = services.BuildServiceProvider())
{
    var loggerFactory = sp.GetService<ILoggerFactory>();
    // ...
}

For configuration details, see the project site.