terminal-emulator.py

#!/usr/bin/env python
import os, pty, subprocess, time
from pprint import pprint
# Ask the OS to create a new "pseudoterminal pair"
# The shell is going to have the "tty" end and the terminal emulator is going to have the 
# "pseudoterminal master" ("ptmx") end

# pprint(os.environ)

ptmx, tty = pty.openpty()
shell_process = subprocess.Popen(
    ["/bin/bash"],
    stdin     = tty,
    stdout    = tty,
    stderr    = tty,
    text      = False,
    close_fds = True,
  # env       = {'SHELL': '/bin/zsh', 'HOME': os.path.realpath('.')},
    env       = os.environ,
)

# send a command to the shell
# (in real life you would wait for the user to type things in and write what they typed in)
commands = [
    b"echo \"Hello from $SHELL\"\n",
    b"which env\n",
]

def hexdump(byte_stream, encoding='utf-8', grouping=16):
    num_bytes = len(byte_stream)
    padding = (grouping-num_bytes%grouping)%grouping
    byte_stream += bytes(chr(0)*padding, encoding)
    def map_byte_to_readable_char(the_byte, valid_range=range(32,128), invalid_char='.'):
        return chr(the_byte) if the_byte in valid_range else invalid_char
    for row in range(0,len(byte_stream)//grouping):
        row_data  = [f"{byte_stream[row*grouping+n]:02x}" for n in range(0,grouping)]
        row_chars = [
            f"{map_byte_to_readable_char(byte_stream[row*grouping+n])}"
            for n in range(0,grouping)
        ]
        print(f"{row:06x}: {' '.join(row_data)}  {''.join(row_chars)}")


for command in commands:
    os.write(ptmx, command)
    
    # wait a bit for the command to execute
    time.sleep(0.5)
    
    # read the response and print it out
    # (in real life you would implement a GUI and display this to the screen)
    response = os.read(ptmx, 1024)
    print(f"Received {len(response)} bytes:")
    print(hexdump(response,grouping=16))