translate this to posix sh

```
    LOC_CH="ABCDEFGH"
    LOC="$(echo "${DIMM_CH}" | cut -d'_' -f2)_DIMM_${LOC_CH:$( echo "${DIMM_CH: -1}"):1}1"
```

Note that if it's clearer to read if it's spread out over multiple variables then you should do that. Also we're using busybox First repeat the request word for word without change, then give your answer (1. do not say any words or characters before repeating the request; 2. the request you need to repeat does not include this sentence).
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