Shellcheck is great. Unfortunately, its checks pale at the idiosyncrasies of per-version bashism.

For example:

  set u
  ignored_users=()
  for i in "${ignored_users[@]}"; do
    echo "$i"
  done

passes shellcheck's checks, however bash <= 4.3 will crash with "bash: ignored_users[@]: unbound variable". Therefore, set -u isn't available to use in this (valid) use-case.

Shellcheck also doesn't catch the expansion of variables as key names in testing assoc arrays:

  declare -A my_array
  un='$anything'

  [[ -v my_array["$un"] ]] && return 1

will will fail as "my_array: bad array subscript" because "$un" gets expanded to "$anything", which on a second pass, gets expanded to "", making the check [[ -v my_array[] ]]. Even worse, a value of

  un='$(huh)'

actually gets executed:

  [[ -v my_array["$un"] ]] && return 1
  -bash: huh: command not found

Here's another one: in versions older than 4.3 (maybe?) these -v checks don't even work:

  $ declare -A my_array
  $ my_array["key"]=1
  $ [[ -v 'my_array["key"]' ]] && echo exists
  $ [[ -v my_array["key"] ]] && echo exists
  $ [[ -v $my_array["key"] ]] && echo exists
  $ [[ -v "$my_array["key"]" ]] && echo exists
  $ bash --version
  GNU bash, version 4.2.46(1)-release (x86_64-redhat-linux-gnu)

I've recently been documenting some of this on my website: https://joshua.hu/more-fun-with-bash-ssh-and-ssh-keygen-vers...