
``pty`` --- Pseudo-terminal utilities
*************************************

*Platforms: *Linux

The ``pty`` module defines operations for handling the pseudo-terminal
concept: starting another process and being able to write to and read
from its controlling terminal programmatically.

Because pseudo-terminal handling is highly platform dependent, there
is code to do it only for Linux. (The Linux code is supposed to work
on other platforms, but hasn't been tested yet.)

The ``pty`` module defines the following functions:

pty.fork()

   Fork. Connect the child's controlling terminal to a pseudo-
   terminal. Return value is ``(pid, fd)``. Note that the child  gets
   *pid* 0, and the *fd* is *invalid*. The parent's return value is
   the *pid* of the child, and *fd* is a file descriptor connected to
   the child's controlling terminal (and also to the child's standard
   input and output).

pty.openpty()

   Open a new pseudo-terminal pair, using ``os.openpty()`` if
   possible, or emulation code for generic Unix systems. Return a pair
   of file descriptors ``(master, slave)``, for the master and the
   slave end, respectively.

pty.spawn(argv[, master_read[, stdin_read]])

   Spawn a process, and connect its controlling terminal with the
   current process's standard io. This is often used to baffle
   programs which insist on reading from the controlling terminal.

   The functions *master_read* and *stdin_read* should be functions
   which read from a file descriptor. The defaults try to read 1024
   bytes each time they are called.


Example
=======

The following program acts like the Unix command *script(1)*, using a
pseudo-terminal to record all input and output of a terminal session
in a "typescript".

   import sys, os, time, getopt
   import pty

   mode = 'wb'
   shell = 'sh'
   filename = 'typescript'
   if 'SHELL' in os.environ:
       shell = os.environ['SHELL']

   try:
       opts, args = getopt.getopt(sys.argv[1:], 'ap')
   except getopt.error as msg:
       print('%s: %s' % (sys.argv[0], msg))
       sys.exit(2)

   for opt, arg in opts:
       # option -a: append to typescript file
       if opt == '-a':
           mode = 'ab'
       # option -p: use a Python shell as the terminal command
       elif opt == '-p':
           shell = sys.executable
   if args:
       filename = args[0]

   script = open(filename, mode)

   def read(fd):
       data = os.read(fd, 1024)
       script.write(data)
       return data

   sys.stdout.write('Script started, file is %s\n' % filename)
   script.write(('Script started on %s\n' % time.asctime()).encode())
   pty.spawn(shell, read)
   script.write(('Script done on %s\n' % time.asctime()).encode())
   sys.stdout.write('Script done, file is %s\n' % filename)
