def get_command(options, vexrc, environ):
    """Get a command to run.

    :returns:
        a list of strings representing a command to be passed to Popen.
    """
    command = options.rest
    if not command:
        command = vexrc.get_shell(environ)
    if command and command[0].startswith('--'):
        raise exceptions.InvalidCommand(
            "don't put flags like '%s' after the virtualenv name."
            % command[0])
    if not command:
        raise exceptions.InvalidCommand("no command given")
    return command
Get a command to run.

    :returns:
        a list of strings representing a command to be passed to Popen.