change json file by bash script

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/.

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 bashjsonFile=$1;node > out_${jsonFile} <<EOF//Read datavar data = require('./${jsonFile}');//Manipulate datadelete data.key3data.key4 = 'new value!';//Output dataconsole.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 nodevar data = require('./'+ process.argv[2]);/*manipulate*/console.log(JSON.stringify(data));

Building off Lenny's answer, we can use node's -p option, which evaluates the given script and writes the output to stdout.

Using the spread operator for easy modification gives:

node -p "JSON.stringify({...require('./data.json'), key4: 'value4'}, null, 2)" > data.json