This used to work: bash-4.4$ a=0 bash-4.4$ echo $(( a[a[0]] )) 0 bash-4.4$ echo ${a[a[a[0]]]} 0
But is broken in bash-5.0: bash-5.0$ a=0 bash-5.0$ echo ${a[a[a[0]]]} bash: a[a[0]]: syntax error: invalid arithmetic operator (error token is "]") bash-5.0$ echo $(( a[a[0]] )) bash: a[a[0]] : syntax error: invalid arithmetic operator (error token is "] ")