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Shell Structure

Explaining the inner workings of all the kernel shells

Shells can be built by implementing two different interfaces and base classes. Why two? Because the shell handler relies on:

  • BaseShell and IShell: To hold shell type and initialization code

  • BaseShellInfo and IShellInfo: To hold shell commands and the base shell

Shell Handler

The shell handler, ShellManager, uses the available shell list, which holds the BaseShellInfo abstract class, to manipulate with that shell. That class can be get, depending on the needed type, with the ShellManager.GetShellInfo() function in the ︎Nitrocid.Shell namespace.

The shell handler also contains two properties: CurrentShellType and LastShellType. The former property holds the current shell type, which can be used with the shell management functions. The latter property holds the last shell type, which is usually the shell that you exited. However, there are three cases:

  • If there are no shells in the shell stack, it returns the primary Shell

  • If there is only one shell in the stack, it returns the current shell as the last one

  • If there are two or more shells in the stack, it returns the last shell type

Additionally, when GetLine() is called, it sets Terminaux's reader history to point to the shell's history list. After it's done getting the input, it reverts back to the General history buffer. They are loaded on boot and saved on shutdown or reboot.

Base Shell

The BaseShell abstract class, which your shell must override, contains the shell type name (ShellType), the flag to bail from the shell (Bail), and the shell initialization code with the shell arguments (InitializeShell()).

public class YourShell : BaseShell, IShell

The shell initialization code usually waits for the Bail value to become true (the shell requested bailing, usually done by exiting the shell using the exit universal command), as in the below example code.

public override void InitializeShell(params object[] ShellArgs)
{
    while (!Bail)
    {
        // Shell code
    }
}

While it's waiting for this to happen, the shell does what it's programmed to do, but in two conditions:

  • All shells must call the ShellManager.GetLine() function, which usually is adaptive to your shell type. This is the below example code inside the shell initialization code to illustrate this:

while (!Bail)
{
    ShellManager.GetLine();
}

  • All shells must also handle both the ThreadInterruptedException, which must set Bail to true, and the general exceptions, which must call continue after dumping the exception to the debugger or to the console. For example, the below example code, inside the InitializeShell() function:

while (!Bail)
{
    try
    {
        ShellManager.GetLine();
    }
    catch (ThreadInterruptedException)
    {
        Bail = true;
    }
    catch (Exception ex)
    {
        TextWriterRaw.WritePlain("There was an error in the shell." + CharManager.NewLine + "Error {0}: {1}", ex.GetType().FullName ?? "<null>", ex.Message);
        continue;
    }
}

The shell registration is required once you're done implementing the shell and all its required values, which will show you how to implement them in the next three pages. The function responsible for this action is ShellTypeManager.RegisterShell() in the Terminaux.Shell.Shells namespace.

Be sure to unregister your shell using the UnregisterShell() function, or the shell registry function will not update your BaseShellInfo class in the available shell lists!

Shell Information

Every BaseShell class you create must accompany it with a separate class that implements the BaseShellInfo and IShellInfo classes, as in below:

internal class YourShellInfo : BaseShellInfo, IShellInfo

This is where your commands get together by overriding the Commands variable with the new dictionary containing all your commands, like below:

public override List<CommandInfo> Commands => new()
{
    new CommandInfo("adduser", /* Localizable */ "Adds users",
        new[] {
            new CommandArgumentInfo(new[]
            {
                new CommandArgumentPart(true, "username"),
                new CommandArgumentPart(false, "password"),
                new CommandArgumentPart(false, "confirm"),
            }, Array.Empty<SwitchInfo>())
        }, new AddUserCommand(), CommandFlags.Strict),
    (...)
};

In addition, you can override the ShellPresets class with a new dictionary containing all the presets for your shell, like below:

public override Dictionary<string, PromptPresetBase> ShellPresets => new()
{
    { "Default", new DefaultPreset() }
};

ShellBase, however, must be overridden with an instance of your shell in this form:

public override BaseShell ShellBase => new YourShell();

Additionally, CurrentPreset must be overridden with a variable that queries your shell type with the CurrentPresets variable as in below:

public override PromptPresetBase CurrentPreset => PromptPresetManager.CurrentPresets[ShellType];

The ShellType variable found within the BaseShellInfo class is a wrapper for the ShellBase.ShellType variable for easier access. It's not overridable and is defined like this:

public string ShellType => ShellBase.ShellType;

By default, all the shells provide you a multi-line prompt, but if you want your input to be in one line wrapped mode, you can override the below property:

public override bool OneLineWrap => false;

If your shell meets the following conditions:

  • You need to handle written text in a way, and

  • You need to use your commands with a slash character,

Then, you need to override the two properties in order for your special non-slash handler to execute:

public override bool SlashCommand => true;
public override CommandInfo NonSlashCommandInfo => new CommandInfo(...);

If you need to know how to define a command information class, consult here.

Base Command

The base command is required to be implemented, since it contains overridable command execution code. Your command must implement the command base class below:

class YourCommand : BaseCommand, ICommand

The only function that you need to override is Execute(), which you can override like below:

public override void Execute(CommandParameters parameters, ref string variableValue)

To support dumb consoles that don't support positioning or complex console functions, you can override ExecuteDumb():

public override void ExecuteDumb(CommandParameters parameters, ref string variableValue)

Additionally, you can override the extra help function, HelpHelper(), like this:

public override void HelpHelper()

If you want to support redirection or wrapping, you must either take dumb console support into account on the Execute() function by not calling any of the below console wrappers, or you must override the ExecuteDumb() function shown above to be compatible with the dumb consoles.

The following wrappers should not be called (explicitly and implicitly) on that function:

  • CursorLeft (set)

  • CursorTop (set)

  • ForegroundColor

  • BackgroundColor

  • CursorVisible

  • OutputEncoding

  • InputEncoding

  • KeyAvailable

  • Beep()

  • Clear()

  • OpenStandardError()

  • OpenStandardInput()

  • OpenStandardOutput()

  • ReadKey()

  • ResetColor()

  • SetCursorPosition()

  • SetOut()

Registering your command

In order for your command to be usable, your mods are now required to register the commands manually using a function that helps doing this. That function is defined in the CommandManager class.

CommandManager.cs
public static void RegisterCustomCommand(ShellType ShellType, CommandInfo commandBase)
public static void RegisterCustomCommand(string ShellType, CommandInfo commandBase)
public static void RegisterCustomCommands(ShellType ShellType, CommandInfo[] commandBases)
public static void RegisterCustomCommands(string ShellType, CommandInfo[] commandBases)

Similarly, if your mod is going to stop, you must unregister all your mod commands, including those that it created in the middle of the kernel uptime. You can use the following functions:

CommandManager.cs
public static void UnregisterCustomCommand(ShellType ShellType, string commandName)
public static void UnregisterCustomCommand(string ShellType, string commandName)
public static void UnregisterCustomCommands(ShellType ShellType, string[] commandNames)
public static void UnregisterCustomCommands(string ShellType, string[] commandNames)

If you've registered your commands correctly, the help command list should list your mod command that you've registered using one of the RegisterCustomCommand functions.

More?

For guidance on how to define your command, click the below button:

For guidance on how to define and manage your command's switches, click the below button:

For information about the help system and how it works, consult the below page:

For command parsing, click the below button:

For shell presets, click the below button:

For command aliasing, click the below button:

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