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Editorial Team
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Asked: 2026-05-31T19:30:34+00:00

I am writing a Python program which runs a virtual terminal. Currently I am

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I am writing a Python program which runs a virtual terminal. Currently I am launching it like so:

import pexpect, thread

def create_input(child, scrollers, textlength=80, height=12):
    while 1:
        newtext = child.readline()
        print newtext

child = pexpect.spawn("bash", timeout=30000)

thread.start_new_thread(create_input,(child))

This works, and I can send commands to it via child.send(command). However, I only get entire lines as output. This means that if I launch something like Nano or Links, I don’t receive any output until the process has completed. I also can’t see what I’m typing until I press enter. Is there any way to read the individual characters as bash outputs them?

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1 Answer

  1. Editorial Team

    The problem is lies in something else. If you open an interactive shell normally a terminal window is opened that runs bash, sh, csh or whatever. See the word terminal!

    In the old days, we connected a terminal to a serial port (telnet does the same but over ip), again the word terminal.

    Even a dumb terminal respond to ESC codes, to report its type and to set the cursor position, colors, clear screen etc.

    So you are starting a subprocess with interactive output, but there is no way in telling that shell and subprocesses are to a terminal in this setup other than with bash startup parameters if there are any.

    I suggest you enable telnetd but only on localhost (127.0.0.1)
    Within your program, make a socket and connect to localhost:telnet and look up how to emulate a proper terminal. If a program is in line mode you are fine but if you go to full screen editing, somewhere you will need an array of 80×24 or 132×24 or whatever size you want to store its characters, color. You also need to be able to shift lines up in that array.

    I have not looked but I cannot imagine there is no telnet client example in python, and a terminal emu must be there too!

    Another great thing is that telnet sessions clean up if the the ip connection is lost, eliminating ghost processes.

    Martijn

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