How to do parse json array dynamically in shell script using jq too in shell script

Question

Suppose I have the following json in a file json.txt

{
  "first_name": "John",
  "last_name": "Smith",
  "things_carried": [
    "apples",
    "hat",
    "harmonica"
  ],
  "children": [
    {
      "first_name": "Bobby Sue",
      "last_name": "Smith"
    },
    {
      "first_name": "John Jr",
      "last_name": "Smith"
    }
  ]
}

In shell script I had written the logic to find the size of children array using jq tool .

size=cat json.txt | jq '.children | length'    
i=0

while [ $i -le $size ]    
do
    array[$i]=$(cat json.txt | jq '.children[$i]')
    i=`expr $i + 1`
done

On running this it gives the following error -

.children[$i]          1 compile error

It seems that it is not able to replace the variable i in the children[] array , as because if we give the expression -

array[$i]=$(cat json.txt | jq '.children[0]')

it runs well .

Can someone help me .

size=cat json.txt | jq '.children | length' will not do what you want. You need to use command substitution — hek2mgl
– hek2mgl, Commented Aug 12, 2015 at 16:32
size=cat json.txt | jq '.children | length,it will give the length of children array . Now through a loop I want to assign each json object inside the children[] array to another array variable — user1483747
– user1483747, Commented Aug 12, 2015 at 16:38
$size is giving correct value = 2 . The problem lies in the jq tool . If we give shell variable inside the jq tool , jq fails to parse . — user1483747
– user1483747, Commented Aug 12, 2015 at 17:19

user3899165 · Accepted Answer · 2015-08-12 17:48:54Z

2

You're using single quotes around the jq program. Shells do not interpolate variables inside single quotes; this is intentional and the jq manual recommends using single quotes around programs for this reason.

An argument syntax is provided by jq for this purpose. This syntax allows you to set jq variables to the value of shell variables. You could replace your current jq invocation with this:

array[$i]=$(cat json.txt | jq --arg i $i '.children[$i | tonumber]')

answered Aug 12, 2015 at 17:48

user3899165

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3 Comments

AndyFaizan Over a year ago

--arg would make jq interpret the value of $i as a string. One should use --argjson flag instead for the value of $i to be read

user3899165 Over a year ago

Agreed! In the code above, I use tonumber to work around that. I'm pretty sure that jq 1.5 hadn't been released yet, hence why I didn't used --argjson.

AndyFaizan Over a year ago

Oh I actually missed the tonumber and yeah I figured that jq 1.5 wasn't probably out then :-)

Jeff Mercado · Accepted Answer · 2015-08-12 18:27:04Z

1

It looks like you're just trying to set the children to a bash array variable.

You don't need to loop, just set the array directly.

$ IFS=$'\n'; array=($(jq -c '.children[]' json.txt))

answered Aug 12, 2015 at 18:27

Jeff Mercado

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Comments

Plínio César · Accepted Answer · 2015-08-12 21:48:38Z

-1

You should use the following syntax:

array[$i]=$(cat json.txt | jq '.children['${i}']')

edited Aug 12, 2015 at 21:48

Plínio César

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answered Aug 12, 2015 at 17:47

user1916693

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