# 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 `shell` is so complex, you might want to read the detailed help.

    >>> command = cli('mailman.commands.cli_withlist.shell')

    >>> command('mailman shell --details')
    This script provides you with a general framework for interacting with a
    mailing list.
    ...

## Running a function

By putting a Python function somewhere on your `sys.path`, you can have `shell` call that function on a given mailing list.

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

The function takes at least a single argument, the mailing list.

    >>> with open(os.path.join(config.VAR_DIR, 'showme.py'), 'w') as fp:
    ...     print("""\
    ... def showme(mlist):
    ...     print("The list's name is", mlist.fqdn_listname)
    ...
    ... def displayname(mlist):
    ...     print("The list's display name is", mlist.display_name)
    ...
    ... def changeme(mlist, display_name):
    ...     mlist.display_name = 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('ant@example.com')
    >>> command('mailman shell -l ant@example.com --run showme')
    The list's name is ant@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.

    >>> command('mailman shell -l ant@example.com --run showme.displayname')
    The list's display name is Ant

## Passing arguments

Your function can also accept an arbitrary number of arguments. Every command line argument after the callable name is passed as a positional argument to the function. For example, to change the mailing list’s display name, you can do this:

    >>> command('mailman shell -l ant@example.com --run showme.changeme ANT!')
    >>> print(mlist.display_name)
    ANT!

## 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')

    >>> command('mailman shell --run showme.displayname -l ^.*example.com')
    The list's display name is ANT!
    The list's display name is Badboys
    The list's display name is Badger

    >>> command('mailman shell --run showme.displayname -l ^bad.*')
    The list's display name is Badboys
    The list's display name is Badger

    >>> command('mailman shell --run showme.displayname -l ^foo')

## 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.