Execute bash command in Node.js and get exit code

Question

I can run a bash command in node.js like so:

var sys = require('sys')
var exec = require('child_process').exec;

function puts(error, stdout, stderr) { sys.puts(stdout) }
exec("ls -la", function(err, stdout, stderr) {
  console.log(stdout);
});

How do I get the exit code of that command (ls -la in this example)? I've tried running

exec("ls -la", function(err, stdout, stderr) {
  exec("echo $?", function(err, stdout, stderr) {
    console.log(stdout);
  });
});

This somehow always returns 0 regardless of the the exit code of the previous command though. What am I missing?

your first example is already giving you the stdout in the console.log — Manatax
– Manatax, Commented Jun 9, 2016 at 17:24

Joe · Accepted Answer · 2016-06-09 17:24:56Z

70

Those 2 commands are running in separate shells.

To get the code, you should be able to check err.code in your callback.

If that doesn't work, you need to add an exit event handler

e.g.

dir = exec("ls -la", function(err, stdout, stderr) {
  if (err) {
    // should have err.code here?  
  }
  console.log(stdout);
});

dir.on('exit', function (code) {
  // exit code is code
});

answered Jun 9, 2016 at 17:24

Joe

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2 Comments

Marc Bacvanski Over a year ago

Awesome! The exit event handler works great; err.code only returns a number if the error code is not 0.

Joshua Robinson Over a year ago

Also execSync(command[, options]) for those interested in the synchronous version. nodejs.org/api/…

Andreas Louv · Accepted Answer · 2016-06-09 17:25:49Z

From the docs:

If a callback function is provided, it is called with the arguments (error, stdout, stderr). On success, error will be null. On error, error will be an instance of Error. The error.code property will be the exit code of the child process while error.signal will be set to the signal that terminated the process. Any exit code other than 0 is considered to be an error.

So:

exec('...', function(error, stdout, stderr) {
  if (error) {
    console.log(error.code);
  }
});

Should work.

Ciro Santilli OurBigBook.com · Accepted Answer · 2019-12-07 07:10:52Z

child_process.spawnSync()

This function exposes the nicest sync interface: https://nodejs.org/api/child_process.html#child_process_child_process_spawnsync_command_args_options

Example:

#!/usr/bin/env node

const child_process = require('child_process');
let out;

out = child_process.spawnSync('true');
console.log('status: ' + out.status);
console.log('stdout: ' + out.stdout.toString('utf8'));
console.log('stderr: ' + out.stderr.toString('utf8'));
console.log();

out = child_process.spawnSync('false');
console.log('status: ' + out.status);
console.log('stdout: ' + out.stdout.toString('utf8'));
console.log('stderr: ' + out.stderr.toString('utf8'));
console.log();

out = child_process.spawnSync('echo', ['abc']);
console.log('status: ' + out.status);
console.log('stdout: ' + out.stdout.toString('utf8'));
console.log('stderr: ' + out.stderr.toString('utf8'));
console.log();

Output:

status: 0
stdout: 
stderr: 

status: 1
stdout: 
stderr: 

status: 0
stdout: abc

stderr:

Tested in Node.js v10.15.1, Ubuntu 19.10.

joe · Accepted Answer · 2021-10-13 13:06:13Z

If anyone is looking for an await/Promise version:

const exec = require('util').promisify(require('child_process').exec);

let out = await exec(`echo hello`).catch(e => e);

console.log(out.stdout); // outputs "hello"
console.log(out.code); // Note: `out.code` is *undefined* if successful (instead of 0).

If the command is successful, then the it'll output an object like {stderr, stdout}. If it has a non-zero exit code, then it'll output an error object with {stderr, stdout, code, killed, signal, cmd} and the usual JavaScript Error object properties like message and stack.

Borja Tur · Accepted Answer · 2016-06-09 17:25:36Z

1

In node documentation i found this information for the callback function:

On success, error will be null. On error, error will be an instance of Error. The error.code property will be the exit code of the child process while error.signal will be set to the signal that terminated the process. Any exit code other than 0 is considered to be an error.

answered Jun 9, 2016 at 17:25

Borja Tur

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