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1:mod:`pty` --- Pseudo-terminal utilities
2========================================
3
4.. module:: pty
5   :platform: Linux
6   :synopsis: Pseudo-Terminal Handling for Linux.
7
8.. moduleauthor:: Steen Lumholt
9.. sectionauthor:: Moshe Zadka <moshez@zadka.site.co.il>
10
11**Source code:** :source:`Lib/pty.py`
12
13--------------
14
15The :mod:`pty` module defines operations for handling the pseudo-terminal
16concept: starting another process and being able to write to and read from its
17controlling terminal programmatically.
18
19Because pseudo-terminal handling is highly platform dependent, there is code to
20do it only for Linux. (The Linux code is supposed to work on other platforms,
21but hasn't been tested yet.)
22
23The :mod:`pty` module defines the following functions:
24
25
26.. function:: fork()
27
28   Fork. Connect the child's controlling terminal to a pseudo-terminal. Return
29   value is ``(pid, fd)``. Note that the child  gets *pid* 0, and the *fd* is
30   *invalid*. The parent's return value is the *pid* of the child, and *fd* is a
31   file descriptor connected to the child's controlling terminal (and also to the
32   child's standard input and output).
33
34
35.. function:: openpty()
36
37   Open a new pseudo-terminal pair, using :func:`os.openpty` if possible, or
38   emulation code for generic Unix systems. Return a pair of file descriptors
39   ``(master, slave)``, for the master and the slave end, respectively.
40
41
42.. function:: spawn(argv[, master_read[, stdin_read]])
43
44   Spawn a process, and connect its controlling terminal with the current
45   process's standard io. This is often used to baffle programs which insist on
46   reading from the controlling terminal.
47
48   The functions *master_read* and *stdin_read* should be functions which read from
49   a file descriptor. The defaults try to read 1024 bytes each time they are
50   called.
51
52   .. versionchanged:: 3.4
53      :func:`spawn` now returns the status value from :func:`os.waitpid`
54      on the child process.
55
56Example
57-------
58
59.. sectionauthor:: Steen Lumholt
60
61The following program acts like the Unix command :manpage:`script(1)`, using a
62pseudo-terminal to record all input and output of a terminal session in a
63"typescript". ::
64
65    import argparse
66    import os
67    import pty
68    import sys
69    import time
70
71    parser = argparse.ArgumentParser()
72    parser.add_argument('-a', dest='append', action='store_true')
73    parser.add_argument('-p', dest='use_python', action='store_true')
74    parser.add_argument('filename', nargs='?', default='typescript')
75    options = parser.parse_args()
76
77    shell = sys.executable if options.use_python else os.environ.get('SHELL', 'sh')
78    filename = options.filename
79    mode = 'ab' if options.append else 'wb'
80
81    with open(filename, mode) as script:
82        def read(fd):
83            data = os.read(fd, 1024)
84            script.write(data)
85            return data
86
87        print('Script started, file is', filename)
88        script.write(('Script started on %s\n' % time.asctime()).encode())
89
90        pty.spawn(shell, read)
91
92        script.write(('Script done on %s\n' % time.asctime()).encode())
93        print('Script done, file is', filename)
94