Configure Serilog File sink to use one log file per application run

Question

I want to configure Serilog to create one log file per app run.
File name should be based on current date/time:
1st run: log_20180413_1020.txt
2nd run: log_20180413_1033.txt

I didn't find how to do it in any File sink (Rolling, Alternative..)
Any clue?

Answer 1

Configure the Serilog.Sinks.File sink without any rolling period or size limit, and add the timestamp to the log filename when you configure logging at startup:

string timestamp = DateTime.Now.ToString("yyyyMMdd_HHmm");
var log = new LoggerConfiguration()
    .WriteTo.File($"log{timestamp}.txt")
    .CreateLogger();

Per the Rolling Policies section of the README:

Specifying both rollingInterval and rollOnFileSizeLimit will cause both policies to be applied, while specifying neither will result in all events being written to a single file.

Answer 2

In case someone is still trying to find out how to achieve this from appsettings.json, I've ended up with this workaround:

// Add this line before creating a logger
UpdateLogFilePath(configuration);

// This is your existing Serilog logger creation logic
var logger = new LoggerConfiguration()
    .ReadFrom.Configuration(configuration)
    .CreateLogger();

Implementation of the UpdateLogFilePath method:

private static void UpdateLogFilePath(IConfigurationRoot configuration)
{
    // A configuration key pattern we are going to look for
    string pattern = "^Serilog:WriteTo.*Args:path$";

    foreach (var kvp in configuration.AsEnumerable())
    {
        if (Regex.IsMatch(kvp.Key, pattern, RegexOptions.IgnoreCase) 
            && !string.IsNullOrEmpty(kvp.Value))
        {
            // Format a file path in the logger configuration
            configuration[kvp.Key] = string.Format(kvp.Value, DateTime.Now);
        }
    }
}

Sample of the appsettings.json:

{
  "Serilog": {
    "Using": [ "Serilog.Sinks.File" ],
    "WriteTo": [
      {
        "Name": "File",
        "Args": {
          "path": "log_{0:yyyyMMdd_HHmm}.txt"
        }
      }
    ]
  }
}

Answer 3

This is my approach for Serilog.Sinks.File and Serilog.Settings.Configuration. It's an evolution of the accepted answer, but also using an appsettings.json.

Sample of the appsettings.json:

"Serilog": {
  "Using": [ "Serilog.Sinks.Debug", "Serilog.Sinks.File" ],
  "MinimumLevel": "Debug",
  "WriteTo": {
    "DebugSink": "Debug",
    "FileSink": {
      "Name": "File",
      "Args": {
        "path": "%LOCALAPPDATA%/Company/Application/{timestamp}.log"
      }
    }
  }
}

Please look at how I handle array declaration in the WriteTo - it is on purpose to have an easier to replace a {timestamp} placeholder — details about WriteTo can find in this section.

Now, let's configure the logger using the config from appsettings.json:

var configuration = new ConfigurationBuilder()
    .AddJsonFile("appsettings.json")
    .Build();

const string serilogFileSinkPath = "Serilog:WriteTo:FileSink:Args:path";

if (configuration.GetSection(serilogFileSinkPath).Exists())
{
    var filePath = configuration[serilogFileSinkPath];
    configuration[serilogFileSinkPath] = filePath.Replace("{timestamp}", DateTime.Now.ToString("yyyyMMdd_HHmmss"));
}

Log.Logger = new LoggerConfiguration()
    .ReadFrom.Configuration(configuration)
    .CreateLogger();

The code reads the configuration.
Next, it checks if the given section that contains the file path is present - if yes, then the replacement of the placeholder happens.
Now configuration has all the needed data, so it can be used to configure the logger.