Invalid Command name when command starts with same character as a shortcut.

[xNinjaKittyx]

I don't know if quit already exists in the library, but I have a command do_quit that just exits out of the command line.
And then I use shortcuts to shortcut q -> quit and exit -> quit.

However, doing this results in this error:

ValueError: Invalid command name 'quit': cannot start with a shortcut: @@, ?, !, @, q

[tleonhardt]

So @kmvanbrunt says this is actually a feature ...

If you have a shortcut “q”, then typing quit would actually run quit with an argument of ”uit”.

There would be no way to run any command that starts with q.

[xNinjaKittyx]

Interesting... I feel like as a shortcut that's only useful for a lot of the builtins, but for the original use case of shortcuts it doesn't feel quite as intuitive..

Is there a way to alias commands without having to create new commands that execute the other? There's docs on aliasing within the CLI, but nothing regarding outside the CLI (from what I could tell)

[kmvanbrunt]

@xNinjaKittyx
There is a distinction between shortcuts and aliases that makes shortcuts very convenient. A shortcut does not require a space between it and its arguments. So the following command lines are valid:

• !ls
• ?macro

The parser checks if a command line begins with a shortcut, and if so, splits them as follows:

• ! ls
• ? macro

Because of this, there is no way to run your quit command directly.

Since quit begins with the shortcut q,the parser splits it this way: q uit
At that point, the parser resolves q into quit which results in a final command line of

quit uit

In your case, the behavior was being masked because your quit function probably just ignores the argument uit being passed to it.

If your application had another command that started with q but wasn't related to quit, you would have seen the issue faster. I added the error message to 0.9.16 to prevent this exact problem.

If you still want to type q and run quit, then you want an alias. For your shortcuts, you will run two commands.
alias create q quit
alias create exit quit

You can create these at startup in a few ways:

1. Have a startup script that runs your alias creation commands
2. Run self.runcmds_plus_hooks() with these commands in a list.

You will see the output of the alias creation when the application starts.

Alias 'q' created
Alias 'exit' created

If you don't want to see that output, then redirect the commands to /dev/null or your operating system's equivalent. You can also pass add_to_history=False to self.runcmds_plus_hooks() if you don't want the alias creation commands to be stored in history.

By the way. cmd2 already has a do_quit() method. If ours already does what you need, then you can remove yours.

[xNinjaKittyx]

I tried this approach, and it works fine. I also thought about adding another hook to add some special rules, but figured this is a little easier to read (although not ideal in my opinion).

Is there no way to create aliases using an API rather than running commands on the CLI on boot? (startup script or runcmds_plus_hooks())

[kmvanbrunt]

@xNinjaKittyx
You can call self.do_alias('create q quit'), but that will print to the screen the alias was created.
You can manually edit the dictionary, but it won't get error checked by the _alias_create command.

self.statement_parser.aliases['q'] = 'quit'

There is no Python API wrapping the CLI commands at this time.

[tleonhardt]

@xNinjaKittyx If you are looking for something quick and dirty that you can do at code-time rather than on boot, you can do something like this:

class QuickApp(cmd2.Cmd):
    def __init__(self):
        super().__init__()

    do_q = do_quit  # now "q" is a synonym for "quit"

This just creates a quick and dirty copy of a command with the exact same contents, docstring, etc. We document this approach in our Frontpage README as well as in several examples such as first_app.py. While this "feature" doesn't have a name since it is just using basic Python capabilities, we typically refer to this as a "synonym" command in our comments and documentation.

[xNinjaKittyx]

Cool, I like that one. Thanks everyone.