Skip to content

AppSettings and Environment Variables#

Populate default values using appSettings and environment variables.

These defaults will be shown as the default values in help output.

The values are converted as they would be if entered in the shell.

Collections can be delimited with a comma. eg. apple,banana,orange

Example App#

We'll use the following app for examples below. 

public class Creds
{
    [Option(LongName = "User", ShortName = "u")]
    public string Username{ get;set; }

    [Option(LongName = "Password", ShortName = "p")]
    public Password Password{ get;set; }

    [Option(LongName = "token", ShortName = "t")]
    public Password AccessToken{ get;set; }
}

public class Api
{
    public void Download(Creds creds, string url, FileInfo file) { ... }
    public void Upload(Creds creds, FileInfo file, string url){...}
}

In this app, the upload and download commands can authenticate with username/password or with an access token.

dotnet example.dll upload -u me -p my_password http://mysite.com c:\myfile.txt
or 
dotnet example.dll upload -t my_token http://mysite.com c:\myfile.txt

Environment Variables#

Enable the feature with appRunner.UseDefaultsFromEnvVar().

Use the [EnvVar("key")] to assign the environment variable as the default for the argument.

With our example, if we wanted to load the access token from an environment variable, decorate the argument as

    [EnvVar("ExampleAppAccessToken")]
    [Option(LongName = "token", ShortName = "t")]
    public Password AccessToken{ get;set; }

When the ExampleAppAccessToken environment variable exists, the default will be that value.

AppSettings#

Enable the feature with appRunner.UseDefaultsFromAppSetting(appSettings)

Use the [AppSetting("key")] to assign the app setting as the default for the argument.

    [AppSetting("AccessToken")]
    [Option(LongName = "token", ShortName = "t")]
    public Password AccessToken{ get;set; }

When the ExampleAppAccessToken app setting exists, the default will be that value.

AppSetting By Convention#

Enable the feature with appRunner.UseDefaultsFromAppSetting(appSettings, includeNamingConventions = true)

includeNamingConventions will enable users to provide defaults for all arguments in your app.

Users can set app settings, using argument names and option short or long names as shown in the help as the setting keys. 

<add key="--user" value="me"/>
<add key="-p" value="my_secret"/>
<add key="url" value="http://mysite.com"/>

Any command with these arguments will inherit the default values from the app settings.

To specify defaults for a specific command, prefix the key with the command name.

<add key="upload url" value="http://my-upload-site.com"/>
<add key="upload --password" value="secret1"/>
<add key="download url" value="http://my-download-site.com"/>
<add key="download -p" value="secret2"/>

.Net Core Config#

Enable the feature with appRunner.UseDefaultsFromConfig(...) and use the pattern below

var appConfig = new ConfigurationBuilder()
    .AddJsonFile("appsettings.json", true, true)
    .Build();

var evConfig = new ConfigurationBuilder()
    .AddEnvironmentVariables()
    .Build();

new AppRunner<App>()
    .UseDefaultsFromConfig(DefaultSources.GetValueFunc("AppSetting", 
        key => appConfig[key],
        DefaultSources.AppSetting.GetKeyFromAttribute
        // includeNamingConventions as described above
        DefaultSources.AppSetting.GetKeysFromConvention))
    .UseDefaultsFromConfig(DefaultSources.GetValueFunc("EnvVar", key => evConfig[key]))
    .Run(args)

Creating two different configs allows us to determine the source of the default value for the Parse directive and the CommandLogger

Other Configs#

Enable the feature with appRunner.UseDefaultsFromConfig(arg => ...)

Example: Say we need git .config settings and have a GitConfigService to read them...

Given an app like this

[AttributeUsage(AttributeTargets.Property|AttributeTargets.Parameter)]
public class GitConfigAttribute : Attribute
{
    public string Key {get;}
    public GitConfigAttribute(string key) => Key = key;
}

public class GitConfig : IArgumentModel
{
    [Option]
    [GitConfig("user.name")]
    public string UserName {get;set;}

    [Option]
    [GitConfig("user.option")]
    public string Email {get;set;}
}

public class MyApp
{
    public void FindRepos(GitConfig gitConfig){...}
}

Use the defaults from GitConfigService like this

new AppRunner<MyApp>
    .UseDefaultsFromConfig(arg => 
    {
        var key = argument.CustomAttributes
                          .GetCustomAttribute<GitConfigAttribute>()
                          ?.Key
        return key != null && _gitConfigService.TryGetValue(key, out var value)
            ? new ArgumentDefault("git-config", key, value)
            : null;
    }
    .Run(args);
)

Note

If the config value returns null, it is assumed no default value was found for the argument and it is skipped. Returning null will not clear already defined default values.

Back to top