change json file by bash script

to change a file in place, use the sponge command

echo '{ "k": "old value" }' >f.json

cat f.json | jq '.k = $v' --arg v 'new value' | sponge f.json

see also: jq issue Edit files in place #105

alternative to jq: jaq

echo '{ "k": "old value" }' >f.json

jaq -i '.k = $v' --arg v 'new value' f.json

... but jaq has less features than jq


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));

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/.


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

Tags:

Bash

Json

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