def transform(v):
    """
    Translate environment variables to ones corresponding to keys in the
    configuration.  In particular, env variables may be made with
    "PERI_"+key_name: fftw-threads = PERI_FFTW_THREADS. Each env var
    is later checked to see if it has to do with PERI
    """
    return v.lower().replace('_', '-').replace('peri-', '')
