Cannot get output of child_process.spawn with interactive scripts

Question

I cannot get any output in the following code:

var spawn = require('child_process').spawn,
    script = 'ftp',
    child = spawn(script);

child.stdout.on('data', function (data) {
  console.log('stdout: ' + data);
});

child.stderr.on('data', function (data) {
  console.log('stderr: ' + data);
});

child.on('close', function (code) {
  console.log('child process exited with code ' + code);
});

It works for normal scripts such as 'ls', 'pwd' etc. But not for interactive programs such as 'ftp', 'telnet'. Any suggestions?

Edit:

Take another script for example:

#!/usr/bin/env python
name = raw_input("your name>")
print name

When spawn this script, I wish to fetch the prompt "your name>" with the data event, so that I can latter input something into stdin.

The problem is that I got nothing in the data event, and it seemed that none of these events are triggered.

This basically boils down to the fact that telnet and ftp handeling the input and output on their own. Try to find settings for these programs where they could perform their tasks in a kind of standalone mode. — TheHippo
– TheHippo, Commented Dec 11, 2013 at 9:36
Otherwise I would suggest using specific node packages for the tasks: npmjs.org/package/telnet and github.com/mscdex/node-ftp — TheHippo
– TheHippo, Commented Dec 11, 2013 at 9:38

damphat · Accepted Answer · 2013-12-11 10:06:22Z

4

ls, cat is controllable via input output and error stream.

ftp, telnet is controllable indirectly via tty.

The protocol is also base on input/output stream but it is more complicated. You can use available package to handle that protocol.

https://github.com/chjj/pty.js

var pty = require('pty.js');
var term = pty.spawn('ftp', [], options);

term.on('data', function(data) {
  console.log(data);
});

term.write(ftpCmd + '\r');

The author of pty have some interesting examples, he forward pty to web via web socket, including terminal games: https://github.com/chjj/tty.js

answered Dec 11, 2013 at 10:06

damphat

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1 Comment

milahu Over a year ago

pty is abandoned since node 8, there is an active fork at github.com/Microsoft/node-pty

user568109 · Accepted Answer · 2013-12-11 09:39:24Z

In interactive mode there is a command interpreter that reads user input from stdin, then accodingly prints output. So you have to write to stdin to do something. For example add following lines to your code with telnet command:

child.stdin.write('?\n');
child.stdin.write('quit\n');

Output:

stdout: Commands may be abbreviated.  Commands are:

!               cr              mdir            proxy           send
$               delete          mget            sendport        site
account         debug           mkdir           put             size
append          dir             mls             pwd             status
ascii           disconnect      mode            quit            struct
bell            form            modtime         quote           system
binary          get             mput            recv            sunique
bye             glob            newer           reget           tenex
case            hash            nmap            rstatus         trace
ccc             help            nlist           rhelp           type
cd              idle            ntrans          rename          user
cdup            image           open            reset           umask
chmod           lcd             passive         restart         verbose
clear           ls              private         rmdir           ?
close           macdef          prompt          runique
cprotect        mdelete         protect         safe

child process exited with code 0

In fact, if you run ftp command in a Linux shell, there is a prompt: "ftp>". Can I get this prompt from stdout's data event?
I think that is not specific to telnet or ftp. Prompt is for the tty. All it does is it changes the tty environment's PS1 var which holds your prompt. If you want command line interpreter like functionality you should use readline. It has a prompt.
Simply create a readline instance and attach it to your ftp or telnet process, while setting the prompt.

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