bash -uc 'declare -a arr=( [idx]=val );echo ${arr[idx]}'

Binary package hint: bash

imi@most:~$ bash -uc 'declare -a arr=( [idx]=val );echo ${arr[idx]}'
bash: idx: unbound variable
imi@most:~$ bash -c 'declare -a arr=( [idx]=val );echo ${arr[idx]}'
val
imi@most:~$ bash -uc 'idx=dunno;declare -a arr=( [idx]=val );echo ${arr[idx]}'
bash: dunno: unbound variable
imi@most:~$ bash -uc 'idx="";declare -a arr=( [idx]=val );echo ${arr[idx]}'
val

According to bash man page associative arrays are supported, also, you can see the result when not using the -u flag. -u is to get error when trying to retrieve a value from a previously unset variable, so there's no point in getting error here, as idx isn't used as variable at all, it is used as an immediate string constant (e.g. as in `echo idx`) subscript.

ProblemType: Bug
Architecture: i386
Date: Tue Apr 6 01:25:09 2010
DistroRelease: Ubuntu 9.10
Package: bash 4.0-5ubuntu2
ProcEnviron:
 PATH=(custom, user)
 LANG=hu_HU.UTF-8
 SHELL=/bin/bash
ProcVersionSignature: Ubuntu 2.6.31-20.58-generic
SourcePackage: bash
Uname: Linux 2.6.31-20-generic i686