How to Execute Command Line Binaries in Node.js?

Executing Command Line Binaries in Node.js

Executing third-party binaries is an essential task when porting CLI libraries from other languages to Node.js. To achieve this in Node.js, there are several modules available:

child_process.exec

For buffered output, use exec:

const { exec } = require('child_process');
exec('cat *.js bad_file | wc -l', (err, stdout, stderr) => {
  if (err) return; // Node couldn't execute the command

  console.log(`stdout: ${stdout}`);
  console.log(`stderr: ${stderr}`);
});

child_process.spawn

If you prefer to receive output as a stream, use spawn:

const { spawn } = require('child_process');
const child = spawn('ls', ['-lh', '/usr']);

// For text chunks, use `child.stdout.setEncoding('utf8');`
child.stdout.on('data', (chunk) => { /* data in chunks */ });

// Pipe the stream elsewhere
child.stderr.pipe(dest);

child.on('close', (code) => { console.log(`Exited with code ${code}`); });

Synchronous Options

Node.js also provides synchronous counterparts to the exec and spawn functions:

const { execSync } = require('child_process');
let stdout = execSync('ls');

const { spawnSync} = require('child_process');
const child = spawnSync('ls', ['-lh', '/usr']);

console.log('error', child.error);
console.log('stdout ', child.stdout);
console.log('stderr ', child.stderr);

Historical Support

For versions of Node.js prior to ES5, the following methods were commonly used:

// Complete output as a buffer
var exec = require('child_process').exec;
exec('prince -v builds/pdf/book.html -o builds/pdf/book.pdf',
  function(error, stdout, stderr) { // command output in stdout });

// Handling large output chunks with streams
var spawn = require('child_process').spawn;
var child = spawn('prince', ['-v', 'builds/pdf/book.html', '-o', 'builds/pdf/book.pdf']);

// Output in chunks
child.stdout.on('data', (chunk) => { /* data in chunks */ });

// Piping output
child.stdout.pipe(dest);

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