make shell scripts conform to shellcheck standards

[joachimschmidt557]

This basically just includes missing shebangs, some quoting and removing reference to a variable never assigned to.

[jameshadfield]

@tsibley could you check these shebangs are ok with you? (I normally use usr/bin/env bash but that may have its own problems). thanks

[tsibley]

@jameshadfield /bin/bash is basically universal and what I use for Bash shebangs. I'd stick with it.

I would expect /usr/bin/env bash to also work nearly all the time, but the use cases for allowing PATH to determine which bash to run seem vanishingly small and in terms of hardcoding paths it just swaps one for another.