Bash empty array expansion with `set -u`

Question

I\'m writing a bash script which has set -u, and I have a problem with empty array expansion: bash appears to treat an empty array as an unset variable during e

Answer 1

Here are a couple of ways to do something like this, one using sentinels and another using conditional appends:

#!/bin/bash
set -o nounset -o errexit -o pipefail
countArgs () { echo "$#"; }

arrA=( sentinel )
arrB=( sentinel "{1..5}" "./*" "with spaces" )
arrC=( sentinel '$PWD' )
cmnd=( countArgs "${arrA[@]:1}" "${arrB[@]:1}" "${arrC[@]:1}" )
echo "${cmnd[@]}"
"${cmnd[@]}"

arrA=( )
arrB=( "{1..5}" "./*"  "with spaces" )
arrC=( '$PWD' )
cmnd=( countArgs )
# Checks expansion of indices.
[[ ! ${!arrA[@]} ]] || cmnd+=( "${arrA[@]}" )
[[ ! ${!arrB[@]} ]] || cmnd+=( "${arrB[@]}" )
[[ ! ${!arrC[@]} ]] || cmnd+=( "${arrC[@]}" )
echo "${cmnd[@]}"
"${cmnd[@]}"