#! /usr/bin/python

import termios
import fcntl
import sys

if __name__ != '__main__':
  exit

if len(sys.argv) != 2:
  print("Usage: echo XYZ | echo2tty.py /dev/ttyXXX")
  exit(1)

try:
  data = sys.stdin.read()
except:
  print("NO stdin!\necho2tty.py is a filter:\nit reads from stdin and sends the data to the specified terminal.")
  exit(2)

with open(sys.argv[1], 'w') as fd:
#	# Works for our own terminal (/proc/self/fd/0)
#	# But FAILS for any other tty, even owned by us (the same user id)
#	# ("echo 'xxx' > '/dev/pts/2'" does send the data to the device
#	#  although shell process on that terminal ignores it).
#	# They say ioctl(TIOCSTI) requires root privileges
#	# (or CAP_SYS_ADMIN to be more specific,
#	#  but that's usually the same in practice)
#	# BTW, the capabilities(7) man page does NOT mention this fact!
  for c in data:
    fcntl.ioctl(fd, termios.TIOCSTI, c)
  # end for
# end with