evennia/docs/source/Howtos/Howto-Command-Prompt.md

# Adding a Command Prompt

A *prompt* is quite common in MUDs:

    HP: 5, MP: 2, SP: 8
    > 

The prompt display useful details about your character that you are likely to want to keep tabs on at all times. It could be health, magical power, gold and current location. It might also show things like in-game time, weather and so on. 

Traditionally, the prompt (changed or not) was returned with every reply from the server and just displayed on its own line. Many modern MUD clients (including Evennia's own webclient) allows for identifying the prompt and have it appear in a fixed location that gets updated in-place (usually just above the input line). 

## A fixed-location prompt

A prompt is sent using the  `prompt` keyword to the `msg()` method on objects. The prompt will be
sent without any line breaks.

```python
self.msg(prompt="HP: 5, MP: 2, SP: 8")
```
You can combine the sending of normal text with the sending (updating of the prompt):

```python
self.msg("This is a text", prompt="This is a prompt")
```

You can update the prompt on demand, this is normally done using [OOB](../Concepts/OOB.md)-tracking of the relevant
Attributes (like the character's health). You could also make sure that attacking commands update
the prompt when they cause a change in health, for example.

Here is a simple example of the prompt sent/updated from a command class: 

```python
    from evennia import Command

    class CmdDiagnose(Command):
        """
        see how hurt your are

        Usage: 
          diagnose [target]

        This will give an estimate of the target's health. Also
        the target's prompt will be updated. 
        """ 
        key = "diagnose"
        
        def func(self):
            if not self.args:
                target = self.caller
            else:
                target = self.caller.search(self.args)
                if not target:
                    return
            # try to get health, mana and stamina
            hp = target.db.hp
            mp = target.db.mp
            sp = target.db.sp

            if None in (hp, mp, sp):
                # Attributes not defined          
                self.caller.msg("Not a valid target!")
                return 
             
            text = f"You diagnose {target} as having {hp} health, {mp} mana and {sp} stamina."
            prompt = f"{hp} HP, {mp} MP, {sp} SP"
            self.caller.msg(text, prompt=prompt)
```
## A prompt with every command

The prompt sent as described above uses a standard telnet instruction (the Evennia web client gets a special flag). Most MUD telnet clients will understand and allow users to catch this and keep the prompt in place until it updates. So *in principle* you'd not need to update the prompt every command.

However, with a varying user base it can be unclear which clients are used and which skill level the users have. So sending a prompt with every command is a safe catch-all. You don't need to manually go in and edit every command you have though. Instead you edit the base command class for your custom commands (like `MuxCommand` in your `mygame/commands/command.py` folder) and overload the `at_post_cmd()` hook. This hook is always called *after* the main `func()` method of the Command.

```python
from evennia import default_cmds

class MuxCommand(default_cmds.MuxCommand):
    # ...
    def at_post_cmd(self):
        "called after self.func()."
        caller = self.caller        
        prompt = f"{caller.db.hp} HP, {caller.db.mp} MP, {caller.db.sp} SP"
        caller.msg(prompt=prompt)

```

### Modifying default commands

If you want to add something small like this to Evennia's default commands without modifying them directly the easiest way is to just wrap those with a multiple inheritance to your own base class:

```python
# in (for example) mygame/commands/mycommands.py

from evennia import default_cmds
# our custom MuxCommand with at_post_cmd hook
from commands.command import MuxCommand

# overloading the look command
class CmdLook(default_cmds.CmdLook, MuxCommand):
    pass
```

The result of this is that the hooks from your custom `MuxCommand` will be mixed into the default
`CmdLook` through multiple inheritance. Next you just add this to your default command set:

```python
# in mygame/commands/default_cmdsets.py

from evennia import default_cmds
from commands import mycommands

class CharacterCmdSet(default_cmds.CharacterCmdSet):
    # ...
    def at_cmdset_creation(self):
        # ...
        self.add(mycommands.CmdLook())
```

This will automatically replace the default `look` command in your game with your own version.