Node.js: Process Spawn Hang

Question

I am trying to run the following shell command:

netstat -nat | grep 3000

and eventually

netstat -nat | grep 3000 | grep ESTABLISHED

from Node.js to obtain ip address connected to specific port using spawn according to https://nodejs.org/api/child_process.html#child_process_child_process_spawn_command_args_options visible below:

const netStat = spawn('netstat', ['-nat']);
const grep = spawn('grep', ['3000']);

netStat.stdout.on('data', (data) => {
  grep.stdin.write(data);
});

console.log('Determining public ip\'s connected to port 3000');
grep.stdout.on('data', function(data){
  console.log(data.toString());
});

But the result just hangs, am I doing something wrong? Thanks in advance for the help!

Handle all the events, probably missing stuff from `stderr`? — Cody Ｇ, Oct 17 '18 at 19:44
Why is that, that you have to handle all the events? - It worked — Sterling Butters, Oct 17 '18 at 19:50
Not saying you _have_ to, sorry --- it was more of a statement on "hopefully this will show you why it's failing", but I'm glad it fixed your error LOL --- What node version are you running? — Cody Ｇ, Oct 17 '18 at 19:53
My guess is that it can't open anything to pipe output to stderr so it just continues trying forever — Cody Ｇ, Oct 17 '18 at 19:55

score 1 · Accepted Answer · answered Oct 17 '18 at 21:04

Since you don't read from the stderr pipe and don't ignore stdio using the options, the process hangs because the pipe is still open until read from.

A similar, but unrelated issue is Why is my Node child process that I created via spawn() hanging? .

Node.js: Process Spawn Hang

1 Answers1

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