# Operating on mailing lists

The `shell` (alias: `withlist`) command is a pretty powerful way to operate on mailing lists from the command line. This command allows you to interact with a list at a Python prompt, or process one or more mailing lists through custom made Python functions.

## Getting detailed help

Because `withlist` is so complex, you need to request detailed help.

    >>> from mailman.commands.cli_withlist import Withlist
    >>> command = Withlist()

    >>> class FakeArgs:
    ...     interactive = False
    ...     run = None
    ...     details = True
    ...     listname = []

    >>> class FakeParser:
    ...     def error(self, message):
    ...         print(message)
    >>> command.parser = FakeParser()

    >>> args = FakeArgs()
    >>> command.process(args)
    This script provides you with a general framework for interacting with a
    mailing list.
    ...

## Running a command

By putting a Python function somewhere on your `sys.path`, you can have `withlist` call that function on a given mailing list. The function takes a single argument, the mailing list.

    >>> import os, sys
    >>> old_path = sys.path[:]
    >>> sys.path.insert(0, config.VAR_DIR)

    >>> with open(os.path.join(config.VAR_DIR, 'showme.py'), 'w') as fp:
    ...     print("""\
    ... def showme(mailing_list):
    ...     print("The list's name is", mailing_list.fqdn_listname)
    ...
    ... def displayname(mailing_list):
    ...     print("The list's display name is", mailing_list.display_name)
    ... """, file=fp)

If the name of the function is the same as the module, then you only need to name the function once.

    >>> mlist = create_list('aardvark@example.com')
    >>> args.details = False
    >>> args.run = 'showme'
    >>> args.listname = 'aardvark@example.com'
    >>> command.process(args)
    The list's name is aardvark@example.com

The function’s name can also be different than the modules name. In that case, just give the full module path name to the function you want to call.

    >>> args.run = 'showme.displayname'
    >>> command.process(args)
    The list's display name is Aardvark

## Multiple lists

You can run a command over more than one list by using a regular expression in the listname argument. To indicate a regular expression is used, the string must start with a caret.

    >>> mlist_2 = create_list('badger@example.com')
    >>> mlist_3 = create_list('badboys@example.com')

    >>> args.listname = '^.*example.com'
    >>> command.process(args)
    The list's display name is Aardvark
    The list's display name is Badboys
    The list's display name is Badger

    >>> args.listname = '^bad.*'
    >>> command.process(args)
    The list's display name is Badboys
    The list's display name is Badger

    >>> args.listname = '^foo'
    >>> command.process(args)

## Error handling

You get an error if you try to run a function over a non-existent mailing list.

    >>> args.listname = 'mystery@example.com'
    >>> command.process(args)
    No such list: mystery@example.com

You also get an error if no mailing list is named.

    >>> args.listname = None
    >>> command.process(args)
    --run requires a mailing list name

## Interactive use

You can also get an interactive prompt which allows you to inspect a live Mailman system directly. Through the `mailman.cfg` file, you can set the prompt and banner, and you can choose between the standard Python REPL or IPython.

If the GNU readline library is available, it will be enabled automatically, giving you command line editing and other features. You can also set the `[shell]history_file` variable in the `mailman.cfg` file and when the normal Python REPL is used, your interactive commands will be written to and read from this file.

Note that the `$PYTHONSTARTUP` environment variable will also be honored if set, and any file named by this variable will be read at start up time. It’s common practice to also enable GNU readline history in a `$PYTHONSTARTUP` file and if you do this, be aware that it will interact badly with `[shell]history_file`, causing your history to be written twice. To disable this when using the interactive `shell` command, do something like:

    $ PYTHONSTARTUP= mailman shell

to temporarily unset the environment variable.

### IPython

You can use IPython as the interactive shell by setting the `[shell]use_ipython` variables in your mailman.cfg file to `yes`. IPython must be installed and available on your system

When using IPython, the `[shell]history_file` is not used.