Prefers `bash` over `sh`.
Prefers `bash` over `sh`.

Assuming a bash interactive environment will be correctly formed on login, we
should prefer to probe the environment using a shell that reports itself as
`bash` instead of `sh` which may not source files that set the
environment modules in statements like:

```
case "$is" in
bash) test -s /etc/bash.bashrc.local && . /etc/bash.bashrc.local ;;
ksh)  test -s /etc/ksh.kshrc.local   && . /etc/ksh.kshrc.local ;;
zsh)  test -s /etc/zsh.zshrc.local   && . /etc/zsh.zshrc.local ;;
ash)  test -s /etc/ash.ashrc.local   && . /etc/ash.ashrc.local
esac
test -s /etc/sh.shrc.local && . /etc/sh.shrc.local
```

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