Not able to get value from json using jq when I replace one of the elements with variable - bash

Question

Using jq if I try to get the value of an element using string I am able to get the value. But to make it flexible if I replace it with a variable then it throws error.
data=$(cat <<EOF
{
"my_db_instance_class": {
"sensitive": false,
"type": "string",
"value": "db.t3.medium"
},
"my_db_instance_test": {
"sensitive": false,
"type": "string",
"value": "db.t4.medium"
}
}
EOF
)
#echo $data
keys=$(echo $data | jq -r '. |=keys' | jq '.[]')
#echo $keys
for key in $keys
do
value=$(echo $data | jq --arg k "$key" '.my_db_instance_class.value')
final_value="${final_value}${key}: ${value}"
done
The above code works but it not very static. Below I have replaced my_db_instance_class with a variable
for key in $keys
do
value=$(echo $data | jq --arg k "$key" '.$k.value')
final_value="${final_value}${key}: ${value}"
done
Error message
jq: error: syntax error, unexpected '$' (Unix shell quoting issues?) at <top-level>, line 1:
.$k.value
jq: error: try .["field"] instead of .field for unusually named fields at <top-level>, line 1:
.$k.value
jq: 2 compile errors
jq: error: syntax error, unexpected '$' (Unix shell quoting issues?) at <top-level>, line 1:
.$k.value
jq: error: try .["field"] instead of .field for unusually named fields at <top-level>, line 1:
.$k.value
jq: 2 compile errors
Expected final output of the whole script
"my_db_instance_class": "db.t3.medium""my_db_instance_test":
"db.t3.medium"

Answer 1

It seems like you're first trying to get all the keys, then loop over then to show the key with the relevant value.
We can simplify this using just jq like so:
to_entries[] | "\(.key): \(.value.value)"
This will produce the following output:
my_db_instance_class: db.t3.medium
my_db_instance_test: db.t4.medium
JqPlay Demo
to_entires documentation
String interpolation (\()) documentation