Shebang should be bash since the script is bash

[emiltang]

The script uses bash-isms that are incompatible with POSIX shell. Examples; [[, +=, read -t.

This is easily verifiable by running the script with dash.

This can of course be fixed in two ways:

1. Make bash a dependency and set the shebang to bash.
2. Remove all bash-isms and make it POSIX compliant.

Option 1 is the easiest and not unreasonable in my opinion.