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@kristopherjohnson
Last active May 14, 2024 23:13
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Read JSON from standard input and writes formatted JSON to standard output. Requires Node.js.
#!/usr/bin/env node
// Reads JSON from stdin and writes equivalent
// nicely-formatted JSON to stdout.
var stdin = process.stdin,
stdout = process.stdout,
inputChunks = [];
stdin.resume();
stdin.setEncoding('utf8');
stdin.on('data', function (chunk) {
inputChunks.push(chunk);
});
stdin.on('end', function () {
var inputJSON = inputChunks.join(),
parsedData = JSON.parse(inputJSON),
outputJSON = JSON.stringify(parsedData, null, ' ');
stdout.write(outputJSON);
stdout.write('\n');
});
@Roam-Cooper
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Roam-Cooper commented May 26, 2016

Make inputChunks a string.

stdin.on('data', function (chunk) {
    inputChunks += chunk;
});

Then you don't need to join.

@noway
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noway commented Jan 4, 2017

WARNING: it inserts "," between the chunks.

to fix this replace

    var inputJSON = inputChunks.join(),

with

    var inputJSON = inputChunks.join(""),

@robinsax
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robinsax commented Jun 2, 2018

@Roam-Cooper, I think the join approach is better as it potentially optimizes the concatenation.

@solex16
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solex16 commented May 19, 2021

Using the double quotes in the join()
also fixed this error I was getting:

'SyntaxError: Unexpected token , in JSON at position 65536'

@hasantayyar
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Nodejs readline native utility can be helpful to split the lines if you are streaming line by line.

@newbie-lad
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'is what i am saying

@tomsaleeba
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tomsaleeba commented Jul 5, 2023

Thanks for gist 💪.

Here's a terser version that uses some of the included fixes:

let inputJson = ''
process.stdin.setEncoding('utf8')
process.stdin.on('data', function (chunk) {
  inputJson += chunk
})
process.stdin.on('end', function () {
  const parsedData = JSON.parse(inputJson)
  process.stdout.write(JSON.stringify(parsedData))
})

@aellerton
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Yet another updated and terser version, ready to edit and run!

function readStdin() {
  return new Promise(resolve => {
    let buf = ''
    process.stdin.setEncoding('utf8')
    process.stdin.on('data', chunk => (buf += chunk))
    process.stdin.on('end', () => resolve(buf))
  })
}

async function main() {
  const d = JSON.parse(await readStdin())
  // do stuff with d, then...
  console.log(JSON.stringify(d, null, 2))
}

@danthegoodman
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Here's a oneliner that does the same thing (at least in mac and linux land, not sure about windows):

node -p 'JSON.stringify(JSON.parse(fs.readFileSync(0)),null,2)'

notably, JSON.parse can work off of a buffer and fs.readFileSync(0) reads the zero file descriptor, which is standard input.
Then, node -p is a way to execute and log the output from a statement. You could also write it with a node -e 'console.log(...)' if you would rather be in control of when or how the logging happens.

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