Dynamic Log Filenames

[ltoshea]

I currently am writing to a statically named log file as defined in my serilog config:
<add key="serilog:write-to:File.path" value="%LOCALAPPDATA%\App_Data\Logs\StaticallyNamedLog.log" />
I'd like to be able to change the logfile name at runtime i.e.

<add key="serilog:write-to:File.path" value="%LOCALAPPDATA%\App_Data\Logs\{appname}-Log.log" />

In log4net for example I'd set a log4net global property value for "appname" in code before the settings were read in. This would then get substituted into this path.

    log4net.globalContext.properties["appname"] = "App1"
    log4net.config.xmlConfigurator.configure("log4net.config")

Then in the logfile I'd reference it like so

%property{appname}

This would then get substituted into this path.

I've really tried to find a solution to this but to no avail - can someone offer any advice as to how I might achieve this?

[nblumhardt]

You can use environment variables in Serilog.Settings.AppSettings values, so if you call System.Environment.SetEnvironmentVariable("APPNAME", "Test") at start-up, before reading from configuration, you can use %APPNAME% in the configured file path. HTH!

[ltoshea]

Thanks for your suggestion nblumhardt, this does seem like a possible solution. How about applications that are running in a context that are more confined and cannot set environmental variables. Or if you are using this as a logging class library. Each application using this would set its own environmental variable value to 'appname' and you would get in all kinds of mess.

[nblumhardt]

Thanks for the reply. The same kinds of issues apply to the log4net version, don't they?

I can guess that in some *nix environments SetEnvironmentVariable() might be restricted, but I don't have any examples at hand.

Does this approach work for your current scenario?

[ltoshea]

Unfortunately not, I'm try to use serilog to provide a logging service that is used by multiple applications and would like a single unified configuration. In log4net the 'appname' property would be attached to the context of each logger meaning I can have a singular config across loggers that write to multiple files. If I understand correctly what you mean by an environmental variable, it seems with the current suggestion each logger would overwrite the previous value.

[nblumhardt]

I'm not sure we're on the same page; by definition, wouldn't log4net.globalContext.properties["appname"] = "App1" also overwrite earlier values?

[ltoshea]

I don't believe so, in the case I'm describing each application has it's own log4net context - so each app could have a property called "appname" with different value (i.e. app1, app2, app3 - which would mean logging to three separate log files) They could all share the same configuration file that would have %property{Appname} in.

If we set an environment variable as suggested for serilog it's system wide - so all loggers would pick up this one value, regardless of if they are different applications.

Hopefully I'm making sense (and I'm not incorrect).
Thanks,
Liam

[nblumhardt]

Ah, I think this is where we're misunderstanding each other. Environment.SetEnvironmentVariable() is not system-wide, it's process-wide. HTH!