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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_pkgng_version(jail=None, chroot=None, root=None):
    '''
    return the version of 'pkg'
    '''
    cmd = _pkg(jail, chroot, root) + ['--version']
    return __salt__['cmd.run'](cmd).strip()