Bash - Looping through nested for loop using arrays

Question

I have 1 array and 2 associative array. I want to loop through both associative array using a master array list because i want the code to be maintainable. But i cant seems to get it right.

When i tried to print out the keys value in my associative array the result is always 0.

Below are my sample code

declare -A list_a list_b
list_a=( [a]=1 [b]=2)
list_b=( [c]=3 [d]=4)
master_list=(list_a list_b)

for thelist in "${master_list[@]}"
do
   for key in "${!thelist[@]}"
   do
     #it show be printing out the keys of the associative array
     echo "the key is: $key"
   done
done

Output:
the key is: 0
the key is: 0

Any idea what the problem could be?

Answer 1

To expand array indirection, the string [@] must be part of the variable. It works for the values:

for thelist in "${master_list[@]}" ; do
    reallist=$thelist[@]
    for key in "${!reallist}" ; do
        echo "the key is: $key"
    done
done

For the keys, I don't see a way without eval.

for thelist in "${master_list[@]}" ; do
    eval keys=('"${!'$thelist'[@]}"')
    for key in "${keys[@]}" ; do
        echo "the key is: $key"
    done
done

As far as you're sure the master_list contains only variable names, it should be safe.

Answer 2

It's fun to play with bash, but bash seems to have some issues to follow your imagination ;)

list_a=( 1 2 )
list_b=( 3 4 )

for key in "${list_a[@]}" "${list_b[@]}"; do
  echo "the key is: $key"
done

Output :

the key is: 1
the key is: 2
the key is: 3
the key is: 4