Multidimensional associative arrays in Bash

Question

I'm trying to create a multidimensional associative array but need some help. I have reviewed the page suggested in this SO answer but it confused me even more. So far here is what I have:

The script:

#!/bin/bash
declare -A PERSONS
declare -A PERSON
PERSON["FNAME"]='John'
PERSON["LNAME"]='Andrew'
PERSONS["1"]=${PERSON[@]}
PERSON["FNAME"]='Elen'
PERSON["LNAME"]='Murray'
PERSONS["2"]=${PERSON[@]}
for KEY in "${!PERSONS[@]}"; do
 TMP="${PERSONS["$KEY"]}"
 echo "$KEY - $TMP"
 echo "${TMP["FNAME"]}"
 echo "${TMP["LNAME"]}"
done

The output:

1 - John Andrew
John Andrew
John Andrew
2 - Elen Murray
Elen Murray
Elen Murray

As you can see trying to access a specific index of the $TMP array in the for loop returns the whole array.

[Q] What do I need to do in order to separately access the "FNAME" and "LNAME" indexes of the $TMP array inside the for loop?

Thanks.

Answer 1

You can't do what you're trying to do: bash arrays are one-dimensional

$ declare -A PERSONS
$ declare -A PERSON
$ PERSON["FNAME"]='John'
$ PERSON["LNAME"]='Andrew'
$ declare -p PERSON
declare -A PERSON='([FNAME]="John" [LNAME]="Andrew" )'
$ PERSONS[1]=([FNAME]="John" [LNAME]="Andrew" )
bash: PERSONS[1]: cannot assign list to array member

You can fake multidimensionality by composing a suitable array index string:

declare -A PERSONS
declare -A PERSON

PERSON["FNAME"]='John'
PERSON["LNAME"]='Andrew'
i=1
for key in "${!PERSON[@]}"; do
  PERSONS[$i,$key]=${PERSON[$key]}
done

PERSON["FNAME"]='Elen'
PERSON["LNAME"]='Murray'
((i++))
for key in "${!PERSON[@]}"; do
  PERSONS[$i,$key]=${PERSON[$key]}
done

declare -p PERSONS
# ==> declare -A PERSONS='([1,LNAME]="Andrew" [2,FNAME]="Elen" [1,FNAME]="John" [2,LNAME]="Murray" )'