@ -104,54 +104,53 @@ This is an issue that was discussed in suckless mailing list
<http://lists.suckless.org/dev/1404/20697.html>: <http://lists.suckless.org/dev/1404/20697.html>:
Well, I am going to comment why I want to change the behaviour 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).
of this key. When ASCII was defined in 1968, communication
with computers was done using punched cards, or hardcopy
terminals (basically a typewriter machine connected with the
computer using a serial port). ASCII defines DELETE as 7F,
because, in punched-card terms, it means all the holes of the
card punched; it is thus a kind of 'physical delete'. In the
same way, the BACKSPACE key was a non-destructive backspace,
as on a typewriter. So, if you wanted to delete a character,
you had to BACKSPACE and then DELETE. Another use of BACKSPACE
was to type 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
the BACKSPACE key is located today on common PC keyboards.
All the terminal emulators emulated the difference between
these keys correctly: the backspace key generated a BACKSPACE
(^H) and delete key generated a DELETE (^?).
But a problem arose when Linus Torvalds wrote Linux. Unlike
earlier terminals, the Linux virtual terminal (the terminal
emulator integrated in the kernel) returned a DELETE when
backspace was pressed, due to the VT100 having a DELETE key in
the same position. This created a lot of problems (see [1]
and [2]). Since Linux has become the king, a lot of terminal
emulators today generate a DELETE when the backspace key is
pressed in order to avoid problems with Linux. The result is
that the only way of generating a BACKSPACE on these systems
is by using CONTROL + H. (I also think that emacs had an
important point here because the CONTROL + H prefix is used
in emacs in some commands (help commands).)
From point of view of the kernel, you can change the key From point of view of the kernel, you can change the key
for deleting a previous character with stty erase. When you 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
connect a real terminal into a machine you describe the type
of terminal, so getty configures the correct value of stty
erase for this terminal. In the case of terminal emulators,
however, you don't have any getty that can set the correct
value of stty erase, so you always get the default value. 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.
For this reason, it is necessary to add 'stty erase ^H' to your
profile if you have changed the value of the backspace key.
Of course, another solution is for st itself to modify the
value of stty erase. I usually have the inverse problem:
when I connect to non-Unix machines, I have to press CONTROL +
h to get a BACKSPACE. The inverse problem occurs 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 [1] http://www.ibb.net/~anne/keyboard.html
[2] http://www.tldp.org/HOWTO/Keyboard-and-Console-HOWTO-5.html [2] http://www.tldp.org/HOWTO/Keyboard-and-Console-HOWTO-5.html
Wolfgang Corcoran-Mathe
10 years ago
Roberto E. Vargas Caballero