def _get_shells():
    '''
    Return the valid shells on this system
    '''
    start = time.time()
    if 'sh.last_shells' in __context__:
        if start - __context__['sh.last_shells'] > 5:
            __context__['sh.last_shells'] = start
        else:
            __context__['sh.shells'] = __salt__['cmd.shells']()
    else:
        __context__['sh.last_shells'] = start
        __context__['sh.shells'] = __salt__['cmd.shells']()
    return __context__['sh.shells']
Return the valid shells on this system