Adding/appending objects to a newly created json array with same keys via jq in bash script

Question

I am having a real hard time in attempting to iteratively append new values over a newly created JSON array/file from the same bash script. Consider the following simple script snippet:

echo "Enter name: "
read name
echo "Enter Car Model: "
read car
echo "Enter Colour: "
read colour

echo
jq -n --arg name "$name" --arg car "$car" --arg colour "$colour" '{"profiles":[{"name": $name, "car": $car, "colour": $colour}]}' > model.json
echo
cat model.json | jq .

This outputs:

Enter name:
Joe
Enter Car Model:
BMW
Enter Colour:
Red

{
  "profiles": [
    {
      "name": "Joe",
      "car": "BMW",
      "colour": "Red"
    }
  ]
}

What I want it to eventually do is something like this, dynamically:

Enter name:
Joe
Enter Car Model:
BMW
Enter Colour:
Red

{
  "profiles": [
    {
      "name": "Joe",
      "car": "BMW",
      "colour": "Red"
    },
    {
      "name": "Peter",
      "car": "Nissan",
      "colour": "White"
    }
  ]
}

etc...

I understand I'll need to utilise a loop after the first set of key:value entries, but then how would I append to the newly created model.json file as opposed to overriding the initial values via jq in a bash script?

Many Thanks

peak · Accepted Answer · 2020-12-03 14:17:56Z

1

To append the object, you can use the idiom:

.profiles += [...]

Because of the friendly way jq handles null, the above will also work initially.

Incidentally, you can abbreviate key-value pairs such as

"name": $name

to just the variable name:

$name

Example

For the sake of uniformity, it might make sense to prepopulate model.json with null, e.g.

echo null > model.json

Then you can invoke jq uniformly (without the -n option), e.g.

jq --arg name "$name" --arg car "$car" --arg colour "$colour" '
  .profiles += [{ $name, $car, $colour}]
' model.json | sponge model.json

Caveat: overwriting the input file using sponge without taking precautions has its risks, though in this case they would seem to be small.

edited Dec 3, 2020 at 14:17

answered Dec 1, 2020 at 13:43

peak

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12 Comments

Data Over a year ago

Like this? jq -n --arg name "$name" --arg car "$car" --arg colour "$colour" '.profiles += [{$name, $car, $colour}]' > model.json So when I add my loop between the jq command and the first set of q&a's, the above works but does not append. Simply overrides the first set of values.

Data Over a year ago

Even if I pipe the above with | .profiles += [{$name, $car, $colour}]' Returns the same set of values: ``` { "profiles": [ { "name": "Paul", "car": "Datson", "colour": "Brown" }, { "name": "Paul", "car": "Datson", "colour": "Brown" } ] } ``` Taking the last entry twice.

peak Over a year ago

You should drop the -n option when reading from model.json

Data Over a year ago

Thank you peak. I have utilised the method you've outlined and unfortunately, the code is still outputting one set of values (The last set of entries I've input). No matter how many times I enter values via the loop, only one set is output. I see the logic in the above code, but not sure where I am going wrong.

peak Over a year ago

Are you sure you have removed the -n option? Perhaps you should try the very simplest case first, without using sponge. Add jq debug statements to see what's going on.

|

Data · Accepted Answer · 2020-12-01 22:03:01Z

0

Utilised the method above and still does not append: ie.

Enter name:
Joe
Enter Car Model:
BMW
Enter Colour:
Blue

Add a new entry? (y/n):  y
Enter name:  
Paul
Enter Car Model:  
Nissan
Enter Colour:  
Black

Add a new entry? (y/n):  n



{
  "profiles": [
    {
      "name": "Paul",
      "car": "Nissan",
      "colour": "Black"
    }
  ]
}

edited Dec 1, 2020 at 22:03

answered Dec 1, 2020 at 17:06

Data

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