evennia/docs/source/Components/Batch-Command-Processor.md

# Batch Command Processor


For an introduction and motivation to using batch processors, see [here](./Batch-Processors.md). This
page describes the Batch-*command* processor. The Batch-*code* one is covered [here](Batch-Code-
Processor).

## Basic Usage

The batch-command processor is a superuser-only function, invoked by 

     > @batchcommand path.to.batchcmdfile

Where `path.to.batchcmdfile` is the path to a *batch-command file* with the "`.ev`" file ending.
This path is given like a python path relative to a folder you define to hold your batch files, set
with `BATCH_IMPORT_PATH` in your settings. Default folder is (assuming your game is in the `mygame`
folder) `mygame/world`. So if you want to run the example batch file in
`mygame/world/batch_cmds.ev`, you could use

     > @batchcommand batch_cmds

A batch-command file contains a list of Evennia in-game commands separated by comments. The
processor will run the batch file from beginning to end. Note that *it will not stop if commands in
it fail* (there is no universal way for the processor to know what a failure looks like for all
different commands). So keep a close watch on the output, or use *Interactive mode* (see below) to
run the file in a more controlled, gradual manner.

## The batch file

The batch file is a simple plain-text file containing Evennia commands. Just like you would write
them in-game, except you have more freedom with line breaks.

Here are the rules of syntax of an `*.ev` file. You'll find it's really, really simple:

- All lines having the `#` (hash)-symbol *as the first one on the line* are considered *comments*.
All non-comment lines are treated as a command and/or their arguments.
- Comment lines have an actual function -- they mark the *end of the previous command definition*.
So never put two commands directly after one another in the file - separate them with a comment, or
the second of the two will be considered an argument to the first one. Besides, using plenty of
comments is good practice anyway.
- A line that starts with the word `#INSERT` is a comment line but also signifies a special
instruction. The syntax is `#INSERT <path.batchfile>` and tries to import a given batch-cmd file
into this one. The inserted batch file (file ending `.ev`) will run normally from the point of the
`#INSERT` instruction.
- Extra whitespace in a command definition is *ignored*.  - A completely empty line translates in to
a line break in texts. Two empty lines thus means a new paragraph (this is obviously only relevant
for commands accepting such formatting, such as the `@desc` command).
- The very last command in the file is not required to end with a comment.
- You *cannot* nest another `@batchcommand` statement into your batch file. If you want to link many
batch-files together, use the `#INSERT` batch instruction instead. You also cannot launch the
`@batchcode` command from your batch file, the two batch processors are not compatible.

Below is a version of the example file found in `evennia/contrib/tutorial_examples/batch_cmds.ev`. 

```bash
    #
    # This is an example batch build file for Evennia. 
    #
    
    # This creates a red button
    @create button:tutorial_examples.red_button.RedButton
    # (This comment ends input for @create)
    # Next command. Let's create something. 
    @set button/desc = 
      This is a large red button. Now and then 
      it flashes in an evil, yet strangely tantalizing way. 
    
      A big sign sits next to it. It says:

    
    -----------
    
     Press me! 
    
    -----------

    
      ... It really begs to be pressed! You 
    know you want to! 
    
    # This inserts the commands from another batch-cmd file named
    # batch_insert_file.ev.
    #INSERT examples.batch_insert_file
    
      
    # (This ends the @set command). Note that single line breaks 
    # and extra whitespace in the argument are ignored. Empty lines 
    # translate into line breaks in the output.
    # Now let's place the button where it belongs (let's say limbo #2 is 
    # the evil lair in our example)
    @teleport #2
    # (This comments ends the @teleport command.) 
    # Now we drop it so others can see it. 
    # The very last command in the file needs not be ended with #.
    drop button
```

To test this, run `@batchcommand` on the file: 

    > @batchcommand contrib.tutorial_examples.batch_cmds

A button will be created, described and dropped in Limbo. All commands will be executed by the user
calling the command.

> Note that if you interact with the button, you might find that its description changes, loosing
your custom-set description above. This is just the way this particular object works.

## Interactive mode

Interactive mode allows you to more step-wise control over how the batch file is executed. This is
useful for debugging and also if you have a large batch file and is only updating a small part of it
-- running the entire file again would be a waste of time (and in the case of `@create`-ing objects
you would to end up with multiple copies of same-named objects, for example). Use `@batchcommand`
with the `/interactive` flag to enter interactive mode.

     > @batchcommand/interactive tutorial_examples.batch_cmds

You will see this:

    01/04: @create button:tutorial_examples.red_button.RedButton  (hh for help) 

This shows that you are on the `@create` command, the first out of only four commands in this batch
file. Observe that the command `@create` has *not* been actually processed at this point!

To take a look at the full command you are about to run, use `ll` (a batch-processor version of
`look`). Use `pp` to actually process the current command (this will actually `@create` the button)
-- and make sure it worked as planned. Use `nn` (next) to go to the next command.  Use `hh` for a
list of commands.

If there are errors, fix them in the batch file, then use `rr` to reload the file. You will still be
at the same command and can rerun it easily with `pp` as needed. This makes for a simple debug
cycle. It also allows you to rerun individual troublesome commands - as mentioned, in a large batch
file this can be very useful. Do note that in many cases, commands depend on the previous ones (e.g.
if `@create` in the example above had failed, the following commands would have had nothing to
operate on).

Use `nn` and `bb` (next and back) to step through the file; e.g. `nn 12` will jump 12 steps forward
(without processing any command in between). All normal commands of Evennia should work too while
working in interactive mode.

## Limitations and Caveats

The batch-command processor is great for automating smaller builds or for testing new commands and
objects repeatedly without having to write so much. There are several caveats you have to be aware
of when using the batch-command processor for building larger, complex worlds though.

The main issue is that when you run a batch-command script you (*you*, as in your superuser
character) are actually moving around in the game creating and building rooms in sequence, just as
if you had been entering those commands manually, one by one. You have to take this into account
when creating the file, so that you can 'walk' (or teleport) to the right places in order.

This also means there are several pitfalls when designing and adding certain types of objects. Here
are some examples:

- *Rooms that change your [Command Set](./Command-Sets.md)*: Imagine that you build a 'dark' room, which
severely limits the cmdsets of those entering it (maybe you have to find the light switch to
proceed). In your batch script you would create this room, then teleport to it - and promptly be
shifted into the dark state where none of your normal build commands work ...
- *Auto-teleportation*: Rooms that automatically teleport those that enter them to another place
(like a trap room, for example). You would be teleported away too.
- *Mobiles*: If you add aggressive mobs, they might attack you, drawing you into combat. If they
have AI they might even follow you around when building - or they might move away from you before
you've had time to finish describing and equipping them!

The solution to all these is to plan ahead. Make sure that superusers are never affected by whatever
effects are in play. Add an on/off switch to objects and make sure it's always set to *off* upon
creation. It's all doable, one just needs to keep it in mind.

## Assorted notes

The fact that you build as 'yourself' can also be considered an advantage however, should you ever
decide to change the default command to allow others than superusers to call the processor. Since
normal access-checks are still performed, a malevolent builder with access to the processor should
not be able to do all that much damage (this is the main drawback of the [Batch Code
Processor](./Batch-Code-Processor.md))

- [GNU Emacs](https://www.gnu.org/software/emacs/) users might find it interesting to use emacs'
*evennia mode*. This is an Emacs major mode found in `evennia/utils/evennia-mode.el`. It offers
correct syntax highlighting and indentation with `<tab>` when editing `.ev` files in Emacs. See the
header of that file for installation instructions.
- [VIM](https://www.vim.org/) users can use amfl's [vim-evennia](https://github.com/amfl/vim-evennia)
mode instead, see its readme for install instructions.