Serilog example for logging

examples/Cli/Logging/Program.cs

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+using Logging.Commands;
+using Microsoft.Extensions.DependencyInjection;
+using Serilog;
+using Spectre.Console.Cli;
+
+/*
+ * Dynamically control serilog configuration via command line parameters
+ *
+ * This works around the chicken and egg situation with configuring serilog via the command line.
+ * The logger needs to be configured prior to executing the parser, but the logger needs the parsed values
+ * to be configured. By using serilog.sinks.map we can defer configuration. We use a LogLevelSwitch to control the
+ * logging levels dynamically, and then we use a serilog enricher that has it's state populated via a
+ * Spectre.Console CommandInterceptor
+ */
+
+namespace Logging
+{
+    public class Program
+    {
+        static int Main(string[] args)
+        {
+            // to retrieve the log file name, we must first parse the command settings
+            // this will require us to delay setting the file path for the file writer.
+            // With serilog we can use an enricher and Serilog.Sinks.Map to dynamically
+            // pull this setting.
+            var serviceCollection = new ServiceCollection()
+                .AddLogging(configure =>
+                    configure.AddSerilog(new LoggerConfiguration()
+                        // log level will be dynamically be controlled by our log interceptor upon running
+                        .MinimumLevel.ControlledBy(LogInterceptor.LogLevel)
+                        // the log enricher will add a new property with the log file path from the settings
+                        // that we can use to set the path dynamically
+                        .Enrich.With<LoggingEnricher>()
+                        // serilog.sinks.map will defer the configuration of the sink to be ondemand
+                        // allowing us to look at the properties set by the enricher to set the path appropriately
+                        .WriteTo.Map(LoggingEnricher.LogFilePathPropertyName,
+                            (logFilePath, wt) => wt.File($"{logFilePath}"), 1)
+                        .CreateLogger()
+                    )
+                );
+
+            var registrar = new TypeRegistrar(serviceCollection);
+            var app = new CommandApp(registrar);
+
+            app.Configure(config =>
+            {
+                config.SetInterceptor(new LogInterceptor()); // add the interceptor
+                config.AddCommand<HelloCommand>("hello");
+            });
+
+            return app.Run(args);
+        }
+    }
+}