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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def get_all(limit=''):
    '''
    Return all installed services. Use the ``limit`` param to restrict results
    to services of that type.

    CLI Example:

    .. code-block:: bash

        salt '*' service.get_all
        salt '*' service.get_all limit=upstart
        salt '*' service.get_all limit=sysvinit
    '''
    limit = limit.lower()
    if limit == 'upstart':
        return sorted(_upstart_services())
    elif limit == 'sysvinit':
        return sorted(_sysv_services())
    else:
        return sorted(_sysv_services() + _upstart_services())