Automatic argument retrieval with fallback mechanism

[GeertvanHorrik]

For my own purposes I have created this convenience method. It checks for argument values in the following order:

1. Specified via command line
2. Specified via build server (build server variable)
3. Specified via environment variable

This way we need less explicit variable definitions because most of them are automatically retrieved from the build server (in most cases, people are running cake from a build server and pass in variables already defined in the build server).

It's currently written for continua ci only, but this can easily be extended to other build servers as well and renamed to GetVariable

public string GetContinuaCIVariable(string variableName, string defaultValue)
{
    var argumentValue = Argument(variableName, "non-existing");
    if (argumentValue != "non-existing")
    {
        Information("Variable '{0}' is specified via an argument", variableName);

        return argumentValue;
    }

    if (ContinuaCI.IsRunningOnContinuaCI)
    {
        var buildServerVariables = ContinuaCI.Environment.Variable;
        if (buildServerVariables.ContainsKey(variableName))
        {
            Information("Variable '{0}' is specified via Continua CI", variableName);

            return buildServerVariables[variableName];
        }
    }

    if (HasEnvironmentVariable(variableName))
    {
        Information("Variable '{0}' is specified via an environment variable", variableName);

        return EnvironmentVariable(variableName);
    }

    Information("Variable '{0}' is not specified, returning default value", variableName);    

    return defaultValue;
}

What do you think, is it worth PR-ing?

[RehanSaeed]

I do something like this:

var mygetApiKey = HasArgument("MyGetApiKey") ? 
    Argument<string>("MyGetApiKey") : 
    EnvironmentVariable("MyGetApiKey");

[RehanSaeed]

I've since evolved my script to do this:

public T GetArgument<T>(string name, T defaultValue = default(T), Func<bool> canGetArgument = null, Func<T> getArgument = null)
{
    return HasArgument(name) ? Argument<T>(name) :
        (canGetArgument != null && getArgument != null && canGetArgument()) ? getArgument() :
        EnvironmentVariable(name) != null ? (T)Convert.ChangeType(EnvironmentVariable(name), typeof(T)) :
        defaultValue;
}

// With no default
var releaseNotes = GetArgument<string>("ReleaseNotes");
// With a default value
var configuration = GetArgument<string>("Configuration", "Release");
// With an override from a CI server
var buildNumber = GetArgument<int>("BuildNumber", 1, () => GoCD.IsRunningOnGoCD, () => GoCD.Environment.Pipeline.Counter);

[augustoproiete]

Related Cake addins that try to help in this area:

• Cake.ArgumentHelpers
• Cake.Args

[alekseiko97]

Hello everyone! Is this still a relevant issue as I see that the last change has been made almost 2 years ago?

[vasu2304]

Hi Everyone! Is this issue still open?