Replace variable in JSON file in bash [duplicate] - json

Question

This question already has answers here:
How to replace values in a JSON dictionary with their respective shell variables in jq?
(2 answers)
Closed 6 months ago.
EDIT: I've updated the question as the answers so far are correct but unfortunately I oversimplified the problem to the point that it will likely need a new question entirely. The issue I'm running into is that I need to replace only a part of value, and that having more than one variable causes sed to gobble multiple variables at once.
here's what I've been trying to do:
# test.json
{
"name": "Mr. ${FIRSTNAME} ${LASTNAME}"
}
I'd like to load this file, replace the variable, and store it in a variable:
NAME=Frodo JSON=$(eval "echo \"$(cat test.json)\"")
echo $JSON
I'd like it to print { "name": "Mr. Frodo Baggins" }, however it seems like eval is stripping out the double quotes, producing invalid JSON: { name: Frodo }. Any idea on how I can do this?
I should also mention that this approach seemed the cleanest, as the variables act as a key-value map. The other approach I tried was with an associative array and sed loop, which seems to work:
KEYS=( "FIRSTNAME" "LASTNAME" )
VALUES=( "Frodo" "Baggins" )
JSON=$(cat test.json)
for index in "${!KEYS[#]}"; do
JSON=$(echo "$JSON" | sed -E "s/\\$\{${KEYS[0]}}/${VALUES[0]}/g")
done
echo $JSON
NOTE: I'm aware that eval is a security risk, however this script is for testing purposes only

Answer 1

edit for altered OP
I'd write the script dynamically, rather than eval during runtime.
$: keys=( "FIRSTNAME" "LASTNAME" )
$: values=( "Frodo" "Baggins" )
$: sed "$(for i in "${!keys[#]}"; do echo "s/\${${keys[i]}}/${values[i]}/;"; done)" test.json
{
"name": "Mr. Frodo Baggins"
}
end edit
First, use jq if you can.
That being said...
If you are VERY CAREFUL with your quoting and ORDER of operations, eval isn't needed.
$: JSON="$(NAME=Frodo; sed s/\${NAME}/$NAME/ json)" && echo "--> $JSON <--"
--> {
"name": "Frodo"
} <--
(When testing, remember to unset JSON between runs.) ;)
This does NOT work without the internal semicolon!
$: JSON="$(NAME=Frodo sed s/\${NAME}/$NAME/ json)" && echo "--> $JSON <--"
--> {
"name": ""
} <--
Remember, assigning NAME=Frodo happens on the same parse of the command line, so you can't use $NAME in that pass. It has to either be a subsequent command or a subshell.
This works, because the parse runs in the subshell where the variable has been set, rather than is being set.
$: echo 'sed s/\${NAME}/$NAME/ json' >script
$: JSON="$(NAME=Frodo ./script)" && echo "--> $JSON <--"
--> {
"name": "Frodo"
} <--