A vital tool in the arsenal of every cli lover is jq. This tool is a command line JSON processor that makes querying for information from a json file very easy and seamless.

However, one feature it is lacking , at least as at the time of this writing is in-place editing, i.e. something similar to what is offerred by the stream editor (sed) , which can edit a file and save the result to the same file., consider the example below

Using sed to replace every instance of HELLO with WORLD

$ sed -e 's/HELLO/WORLD' -i input_file.json

To achieve something similar in jq, copy the json document below and save it in a file called unformatted.json

{
"order_num" : "O2012019231a",
"order_date" : "2012-06-27",
"order_id" : 21934,
"order_item" : [
{
"product_id" : 20933,
"quantity" : 3,
"price" : 36000,
"product_name" : "Thingamagic 2000",
"unit_price" : 12000
},
{
"product_id" : 10366,
"quantity" : 1,
"price" : 100,
"product_name" : "Super Duper Blooper",
"unit_price" : 100
}
]
}

Now, to prettify the document (unformatted.json) in place, you have two options, listed below

• Using cat & heredoc
• Using Sponge linux utility

Using Cat & Heredoc

A very simple way to achive in-place editing with jq using cat tool is to understand linux redirection, what we will do is to apply jq to the file, then redirect the output to cat and then finally redirect the output to the same filename as shown below.

$ cat <<< jq '.' unformatted.json > unformatted.json

Explanation

1. <<< – achieves what is called a cat heredoc. It helps to send multilines into the cat tool
2. > – This achieves the second redirection by redirecting the output of the cat tool into the filename supplied.

Using Sponge Linux Utility

This is a simpler workflow and easier to reason through if you are not a big fan of linux redirections and pipes. Firstly, you need to install the sponge tool by doing the following.

#Debian / Ubuntu
apt-get install moreutils

# Fedora flavours
dnf install moreutils

# Windows (WSL2)
sudo apt-get update sudo apt-get install moreutils

Then run the following command

$ jq '.' unformatted.json | sponge unformatted.json

Both of the options explained above, will prettify the file in place and generate the output shown below

{
  "order_num": "O2012019231a",
  "order_date": "2012-06-27",
  "order_id": 21934,
  "order_item": [
    {
      "product_id": 20933,
      "quantity": 3,
      "price": 36000,
      "product_name": "Thingamagic 2000",
      "unit_price": 12000
    },
    {
      "product_id": 10366,
      "quantity": 1,
      "price": 100,
      "product_name": "Super Duper Blooper",
      "unit_price": 100
    }
  ]
}