Better defaults for shell scripts

[BaldPolnareff]

I just added a couple of better defaults for the shell scripts:

1. #!/usr/bin/env bash is usually recommended over hardcoding #!/bin/bash as some systems may have bash in different places, this trick should resolve the env with the right path to bash in general
2. set -euo pipefail guarantees running in strict mode, in case uncaught errors occur, the scripts will exit at the failure point, rather than continuing executing the rest of the script

[al12gamer]

Thanks for these! Any other suggestions?