jq bash Adding a json field to a json file - json

Question

i'm stuck on jq input problem. I have a json file that looks like this:
{
"main_object": {
"child1": ["banana", "apple", "orange"]
}
}
I need to add another child object and rewrite this file, the problem is that this child object needs to be generated dynamically. so i'm doing this:
added_string=$(printf '.main_object += {%s: %s}' "$child_name" "$fruits")
Then I wrote this line, which worked well on my mac shell:
edited_json=$(cat $json_variable_file | jq $added_string)
When i tried to run all of this from a bash script i got this error:
jq: error: Could not open file +=: No such file or directory
jq: error: Could not open file {"child2":: No such file or directory
jq: error: Could not open file ["orange","potato","watermelon"]}: No such file or directory
So I tried many things so far, most of them still give me the same error, also tried doing this:
edited_json=$(cat $json_variable_file | jq <<< $added_string)
The error i got is this:
parse error: Invalid numeric literal at line 1, column 23
Really appreciate your time, the weird thing here is that it works completely fine, generating the needed json on my zsh but it does not work on bash.

Answer 1

With bash and zsh:
child_name="child2"
fruits='["orange","potato","watermelon"]'
added_string=$(printf '.main_object += {%s: %s}' "$child_name" "$fruits")
cat file | jq "$added_string" # quotes are important
Output:
{
"main_object": {
"child1": [
"banana",
"apple",
"orange"
],
"child2": [
"orange",
"potato",
"watermelon"
]
}
}