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Andrés Muñoz
Asked: 2020-01-07 20:30:34 +0800 CST 2020-01-07 20:30:34 +0800 CST

What are tty files for?

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In the Python documentation I came across this method for objects like:

archivo = open('archivo', 'r'); 
archivo.isatty()

which returns True/ Falsewhether the file is a tty or not. and i was wondering

  1. What is a tty file?
  2. What is a tty file used for?

file.isatty()

Return Trueif the file is connected to a tty(-like) device, else False.

Note: If a file-like object is not associated with a real file, this method should not be implemented.

https://docs.python.org/2/library/stdtypes.html?highlight=file%20flush#file.isatty

python

2 Answers

  1. Best Answer

    The function file.isatty( TTY stands for TeleTypewriter , which are electromechanical teleprinters used in the past to connect to terminals), tells you if the file is connected to a TTY-type device.

    In Linux, you can find out the name of the file connected to your STDIN(Standard Input) using the command tty:

    $ tty
/dev/pts/24

    The file /dev/pts/24should be connected to a virtual device:

    >>>  archivo = open('/dev/pts/24')
>>>  archivo.isatty()
True

    Actually the files /dev/pts/Nare pseudo-terminals, that is, those that are created when you have a session from a graphical interface (for example, using gnome-terminal). If you connect to a virtual terminal (the ones you use in full screen) using Ctrl+ Alt+ F1, you can see that the command ttyshows you a different file:

    $ tty
/dev/tty1

    The file /dev/tty1should also be connected to a TTY device:

    >>>  archivo = open('/dev/tty1')
>>>  archivo.isatty()
True

    What is a TTY file?

    In general, the operating system creates some files that allow you to communicate with physical devices, normally these files are located in the folder /devand are treated in a special way since they are allowed to have access to the drivers. TTY files are responsible for displaying information input and output to the terminal (via the keyboard and monitor). You can see a list of them using:

    $ ls -l /dev/tty*
crw-rw-rw- 1 root  tty     5,  0 ene  6 15:36 /dev/tty
crw--w---- 1 root  tty     4,  0 ene  4 06:55 /dev/tty0
crw------- 1 cesar tty     4,  1 ene  7 08:04 /dev/tty1
crw--w---- 1 root  tty     4, 10 ene  4 06:55 /dev/tty10
crw--w---- 1 root  tty     4, 11 ene  4 06:55 /dev/tty11
crw--w---- 1 root  tty     4, 12 ene  4 06:55 /dev/tty12
crw--w---- 1 root  tty     4, 13 ene  4 06:55 /dev/tty13
crw--w---- 1 root  tty     4, 14 ene  4 06:55 /dev/tty14
crw--w---- 1 root  tty     4, 15 ene  4 06:55 /dev/tty15
crw--w---- 1 root  tty     4, 16 ene  4 06:55 /dev/tty16
crw--w---- 1 root  tty     4, 17 ene  4 06:55 /dev/tty17
crw--w---- 1 root  tty     4, 18 ene  4 06:55 /dev/tty18
crw--w---- 1 root  tty     4, 19 ene  4 06:55 /dev/tty19
crw------- 1 cesar tty     4,  2 ene  7 07:54 /dev/tty2
...

    What is a TTY file used for?

    Well, as I mentioned in the first question, they are used by the operating system to allow you to "converse" with physical devices like the keyboard and monitor. Maybe this image will help a bit:

    enter image description here

    References

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  2. ttyit is a physical terminal, with keyboard and screen, or virtual like XTerm. Unlike a normal file, each tty has "properties" such as size (dimensions, width and height), the ability to change colors, and others. In Unix and similar systems like Linux each terminal (physical or virtual) connects to the virtual file, its own tty. They can be found at /dev/: /dev/tty<N>they are for text consoles, and /dev/pts/<N>for terminal emulators like XTerm or Gnome Terminal.

    A program can find out that its stdoutand stderrcorrespond to a ttyand activate a special mode, for eg. eg create an interactive interface with "windows" as Midnight Commanderin Linux/Unix or FAR Commanderin Windows.

    In Python it can be used like this:

    import sys
if sys.stdout.isatty():
    # escribir en rojo
    esc="\x1B["
    rojo=esc + "0;31m"
    normal=esc + "0m"
    print(rojo + "Hello World!" + normal)
else:
    # escribir normal
    print("Hello World!")

    This code writes the text "Hello World!" in red using ANSI escape sequences (in English) if it is executed simply in bash, but with stdoutredirected to a file, it writes the text without special characters.

    It is also possible to send something to a ttyand ttyit will receive it. write and other programs use this feature to send messages to users.

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