Get the project file path

To get the project file path, use the Path property of the IProject object.

public void OutputProjectFilePath(ICommandContext c, ICommandParams p)
{
    //Get the project file path
    var projectFilePath = c.App.Workspace.CurrentProject.Path;
    c.App.Output.WriteLine("sample", projectFilePath);
}

To get the project file directory, use the GetDirectoryName() method of System.IO.Path.

//Get the project file path
var projectFilePath = c.App.Workspace.CurrentProject.Path;

//Get the project file directory
var dir = System.IO.Path.GetDirectoryName(projectFilePath);

App.Output.WriteLine("sample", $"Directory : {dir}");