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Add info about Backspace and Delete to the FAQ

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Roberto E. Vargas Caballero 2014-07-24 19:56:58 +02:00
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@ -98,3 +98,61 @@ If you want to compile st for OpenBSD you have to remove -lrt from config.mk, an
st will compile without any loss of functionality, because all the functions are
included in libc on this platform.
## Backspace key does not work
This is an issue that was discussed in suckless mailing list
<http://lists.suckless.org/dev/1404/20697.html>:
Well, I am going to comment why I want to change the behaviour
of this key. When ascii was defined in 1968 communication
with computers were done using punched cards, or hardcopy
terminals (basically a typewritter machine connected with
the computer using a serial port). Due to this, ascii defines
DELETE as 7F, because in the puched cards, it means all the
holes of the card punched, so it is a kind of 'phisical
delete'. In the same way, BACKSPACE key was a non destructive
back space, as in typewriter machines. So, if you wanted
to delete a character, you had to BACKSPACE and then DELETE.
Other use of BACKSPACE was accented characters, for example
'a BACKSPACE `'. The VT100 had no BACKSPACE key, it was
generated using the CONTROL key as another control character
(CONTROL key sets to 0 b7 b6 b5, so it converts H (code
0x48) into BACKSPACE (code 0x08)), but it had a DELETE key
in a similar position where BACKSPACE key is located today
in common PC keyboards. All the terminal emulators emulated
correctly the difference between these keys, and backspace
key generated a BACKSPACE (^H) and delete key generated a
DELETE (^?).
But the problem arised when Linus Torvald wrote Linux, and
he did that the virtual terminal (the terminal emulator
integrated in the kernel) returns a DELETE when backspace
was pressed, due to the fact of the key in that position
in VT100 was a delete key. This created a lot of problems
(you can see it in [1] and [2]), and how Linux became the
king, a lot of terminal emulators today generate a DELETE
when backspace key is pressed in order to avoid problems
with linux. It causes that the only way of generating a
BACKSPACE in these systems is using CONTROL + H. I also
think that emacs had an important point here because CONTROL
+ H prefix is used in emacs in some commands (help commands).
From point of view of the kernel, you can change the key
for deleting a previous character with stty erase. When you
connect a real terminal into a machine you describe the
type of terminal, so getty configure the correct value of
stty erase for this terminal, but in the case of terminal
emulators you don't have any getty that can set the correct
value of stty erase, so you always get the default value.
So it means that in case of changing the value of the
backspace keyboard, you have to add a 'stty erase ^H' into
your profile. Of course, other solution can be that st
itself modify the value of stty erase. I have usually the
inverse problem, when I connect with non Unix machines, and
I have to press control + h to get a BACKSPACE, or the
inverse, when a user connects to my unix machines from a
different system with a correct backspace key.
[1] http://www.ibb.net/~anne/keyboard.html
[2] http://www.tldp.org/HOWTO/Keyboard-and-Console-HOWTO-5.html