Use of child_process.spawn to pipe data

[targos]

Hello. I would like to the the following using child_process.spawn:

string (input of command 1) -> command1 | command2 | command3 -> string (output of command3)

I wrote a script like that (simplified):

var spawn = require('child_process').spawn;

var cp1 = spawn('/bin/command1', ['arg1', 'arg2'], {stdio: 'pipe'});
var cp2 = spawn('/bin/command2', ['arg1', 'arg2'], {stdio: [cp1.stdout, 'pipe', 'pipe']});
var cp3 = spawn('/bin/command3', ['arg1', 'arg2'], {stdio: [cp2.stdout, 'pipe', 'pipe']});

var result = '';
cp3.stdout.on('data', data => result += data);
cp3.on('close', () => console.log(result));

cp1.stdin.end('mydata');

The problem is I sometimes get the correct result and sometimes it finishes with an empty string (given the same input data).
Am I doing something obviously wrong ?

[addaleax]

Am I doing something obviously wrong ?

If it’s any consolation, no, there’s nothing obviously wrong to me, and the code looks about like what I would have written.

I tried turning your example into a runnable script spawning cat, and it seems to work okay…

[targos]

Closing in favor of nodejs/node#9413