change json file by bash script

Question

I need your help to solve the following problem: I have a JSON file that looks like this:

{   "key1": "value1",   "key2": "value2",   "key3": "value3" } 

how can I add and remove a new key (i.e "key4": "value4") by bash script? I see also the issue to add or remove a comma at the end of last key in the file before adding or removing the new one.

Thank you

Answer 1

Your best bet is to use a JSON CLI such as jq:

• On Debian-based systems such as Ubuntu, you can install it via sudo apt-get install jq
• On macOS, with Homebrew (http://brew.sh/) installed, use brew install jq

Examples, based on the following input string - output is to stdout:

jsonStr='{ "key1": "value1", "key2": "value2", "key3": "value3" }' 

Remove "key3":

jq 'del(.key3)' <<<"$jsonStr" 

Add property "key4" with value "value4":

jq '. + { "key4": "value4" }' <<<"$jsonStr" 

Change the value of existing property "key1" to "new-value1":

jq '.key1 = "new-value1"' <<<"$jsonStr" 

A more robust alternative ^{thanks, Lars Kiesow} :
If you pass the new value with --arg, jq takes care of properly escaping the value:

jq '.key1 = $newVal' --arg newVal '3 " of rain' <<<"$jsonStr" 

---

If you want to update a JSON file in place (conceptually speaking), using the example of deleting "key3":

# Create test file. echo '{ "key1": "value1", "key2": "value2", "key3": "value3" }' > test.json  # Remove "key3" and write results back to test.json (recreate it with result). jq -c 'del(.key3)' test.json > tmp.$$.json && mv tmp.$$.json test.json 

You cannot replace the input file directly, so the result is written to a temporary file that replaces the input file on success.

Note the -c option, which produces compact rather than pretty-printed JSON.

For all options and commands, see the manual at http://stedolan.github.io/jq/manual/.

Answer 2

Not the answer for everyone, but if you already happen to have NodeJs installed in your system, you can use it to easily manipulate JSON.

eg:

#!/usr/bin/env bash jsonFile=$1;  node > out_${jsonFile} <<EOF //Read data var data = require('./${jsonFile}');  //Manipulate data delete data.key3 data.key4 = 'new value!';  //Output data console.log(JSON.stringify(data));  EOF 

Heck, if you only need to do JSON manipulation and you have node (ie: You don't really need any other bash functionality) you could directly write a script using node as the interpreter:

#! /usr/bin/env node var data = require('./'+ process.argv[2]); /*manipulate*/ console.log(JSON.stringify(data));