> to put `-u` (nounset) in your shebang

Any particular reason why in the shebang instead of set -u?

> The only exception I typically run across is expansion of arrays using "${arr[@]}" syntax

In Bash? Works for me. Edit: another comment mentions it as well. Seem to behave better in newer versions of Bash and only problematic in <= 4.3 https://news.ycombinator.com/item?id=38397241

  $ bash -uc 'unset x; echo "=> ${x[@]}"'
  =>
  $ bash -uc 'x=(); echo "=> ${x[@]}"'
  =>
  $ bash -uc 'x=(); echo "=> ${x[0]}"'
  bash: x[0]: unbound variable

Zsh does not like the first example but both should support:

  $ bash -uc 'unset x; echo "=> ${x[@]:-null}"'
  => null

> Also handy is `-e` (errexit),

It is unfortunately very confusion with functions. Made me like it less over the years.