Shell Script: Pick one specific global variable with keyward

Question

There are multiple global variables with same pattern in my shell script like:

VALID_DOMESTIC_ANIMAL=(cat dog)
VALID_ACQUATIC_ANIMAL=(shark dolphin)

Now, There is another argument CATAGORY , which could be ACQUATIC/DOMESTIC. How can I select the expected global variable to iterate ? I tried following code:

#!/bin/bash
VALID_DOMESTIC_ANIMAL=(cat dog)
VALID_ACQUATIC_ANIMAL=(shark dolphin)

CATAGORY=ACQUATIC
VALID_CATAGORY_ANIMAL=VALID_${CATAGORY}_ANIMAL
#echo "VALID_CATAGORY_ANIMAL ${VALID_CATAGORY_ANIMAL}"
for anime in "${VALID_CATAGORY_ANIMAL[@]}"; do
    echo "${anime}"
done

I am expecting output shark dolphin but I am getting VALID_ACQUATIC_ANIMAL

How can I tell bash script that if there exists a variable with same name, use it ?

Answer 1

Thanks steeldriver for showing way forward Varibles - Union . I used nameref and it worked for me. Performing following change did the trick.

-VALID_CATAGORY_ANIMAL=VALID_${CATAGORY}_ANIMAL
+declare -n VALID_CATAGORY_ANIMAL=VALID_${CATAGORY}_ANIMAL

Answer 2

This may make it clearer. This variable contains the name of another variable. To get its value the shell must first expand the variable name and then the variable value.

for anime in $(eval echo \${$VALID_CATAGORY_ANIMAL[@]}); do

eval - It take an arguments expands variables and passes to execute by the shell
Since we escaped the first dollar sign, the command will go to execution in this:

$(echo ${VALID_ACQUATIC_ANIMAL[@]}

You can insert the following line before the loop

echo $VALID_CATAGORY_ANIMAL    #VALID_ACQUATIC_ANIMAL
echo \${$VALID_CATAGORY_ANIMAL[@]}    #${VALID_ACQUATIC_ANIMAL[@]}
eval echo \${$VALID_CATAGORY_ANIMAL[@]}    #shark, dolphin