Execute custom command on nodejs process

Question

I've am totally newbie when it comes for nodejs.

I am writing a custom program, and I need to add a watch in it, for example I start with nodejs a .bat file which is working fine, but I've been wondering is it possible to control execution of commands in that shell process from the outside?

Like I am running the shell process and type in it by hand "refresh; reload resource_1" and it is working properly, but working with nodemon I would like to add a watch for it, example: I edit a file in a src folder, I would like nodejs automatically to type (or execute) into that shell process the "refresh; reload resource_1" and etc. I tried with exec, but it's working with already defined commands like 'kill, dir' and so more.

I am working on a Windows machine.

Thanks in advance.

CherryDT · Accepted Answer · 2020-04-21 20:43:07Z

You can write into the child process' stdin! (Provided that you started it in your own node script.)

const { spawn } = require('child_process')

const child = spawn('some_command') // Start whatever process you want to talk to

// Pipe output so you can see it (you can also instead listen on the stdout/stderr streams
// and capture their output programmatically)
child.stdout.pipe(process.stdout)
child.stderr.pipe(process.stderr)

// Set encoding for input
child.stdin.setEncoding('utf-8')

// Write stuff into the process' stdin!
child.stdin.write('refresh; reload resource_1')

// Note that as long as the process is running and you keep the `child` variable around,
// you can keep writing into `child.stdin` even much later.

Further reading:

If you didn't start the program yourself but you want to automate an already-running program from before, it gets a lot more tricky, and nodejs isn't the best tool for that. There are WinAPI functions you could use but this is its own rabbit hole and it would be a waste of time now to get into it unless you really need it.

Algo7 · Accepted Answer · 2020-04-21 20:30:08Z

0

You can take advantage of the in-built child_processof Node.js


'use strict';
//Dependencies
const { exec, sapwn } = require('child_process');

//The command which you wish to run

//If you want to use PowerShell
//child = spawn("powershell.exe",["c:\\temp\\helloworld.ps1"]);

exec('cat *.js missing_file | wc -l', (error, stdout, stderr) => {

//Logging

  if (error) {
    console.error(`exec error: ${error}`);
    return;
  }

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

Please refer to the official documentation here: https://nodejs.org/api/child_process.html

edited Apr 21, 2020 at 20:30

answered Apr 21, 2020 at 20:09

Algo7

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8 Comments

Ilia Hanev Over a year ago

Thank you, maybe I did this wrong, but I tried and didn't work for me. I start the process shell, save its PID somewhere, then find the process by PID and exec('refresh') on it and it did not work either. What should I replace here by your suggestion? //The command which you wish to run exec('cat *.js missing_file | wc -l') Thanks in advance.

JustAMartin Over a year ago

@IliaHanev Of course, you should replace 'cat *.js missing_file | wc -l' text with your own commands to execute.

Ilia Hanev Over a year ago

@JustAMartin Yes, I did this and it didn't work either.

Algo7 Over a year ago

What's your operating system? If it's windows then the cat command won't work for sure. It's type in Windows. You'll have to adapt the syntax to suit the Windows's shell.

Ilia Hanev Over a year ago

The OS is windows. So I should write exec("type refresh; reload res1") and this should work?

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