@ -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
of this key. When ASCII was defined in 1968, communication
with computers were done using punched cards, or hardcopy
with computers was done using punched cards, or hardcopy
terminals (basically a typewritter machine connected with
terminals (basically a typewriter machine connected with the
the computer using a serial port). Due to this, ascii defines
computer using a serial port). ASCII defines DELETE as 7F,
DELETE as 7F, because in the puched cards, it means all the
because, in punched-card terms, it means all the holes of the
holes of the card punched, so it is a kind of 'phisical
card punched; it is thus a kind of 'physical delete'. In the
delete'. In the same way, BACKSPACE key was a non destructive
same way, the BACKSPACE key was a non-destructive backspace,
back space, as in typewriter machines. So, if you wanted
as on a typewriter. So, if you wanted to delete a character,
to delete a character, you had to BACKSPACE and then DELETE.
you had to BACKSPACE and then DELETE. Another use of BACKSPACE
Other use of BACKSPACE was accented characters, for example
was to type accented characters, for example 'a BACKSPACE `'.
'a BACKSPACE `'. The VT100 had no BACKSPACE key, it was
The VT100 had no BACKSPACE key; it was generated using the
generated using the CONTROL key as another control character
CONTROL key as another control character (CONTROL key sets to
(CONTROL key sets to 0 b7 b6 b5, so it converts H (code
0 b7 b6 b5, so it converts H (code 0x48) into BACKSPACE (code
0x48) into BACKSPACE (code 0x08)), but it had a DELETE key
0x08)), but it had a DELETE key in a similar position where
in a similar position where BACKSPACE key is located today
the BACKSPACE key is located today on common PC keyboards.
in common PC keyboards. All the terminal emulators emulated
All the terminal emulators emulated the difference between
correctly the difference between these keys, and backspace
these keys correctly: the backspace key generated a BACKSPACE
key generated a BACKSPACE (^H) and delete key generated a
(^H) and delete key generated a DELETE (^?).
DELETE (^?).
But a problem arose when Linus Torvalds wrote Linux. Unlike
But the problem arised when Linus Torvald wrote Linux, and
earlier terminals, the Linux virtual terminal (the terminal
he did that the virtual terminal (the terminal emulator
emulator integrated in the kernel) returned a DELETE when
integrated in the kernel) returns a DELETE when backspace
backspace was pressed, due to the VT100 having a DELETE key in
was pressed, due to the fact of the key in that position
the same position. This created a lot of problems (see [1]
in VT100 was a delete key. This created a lot of problems
and [2]). Since Linux has become the king, a lot of terminal
(you can see it in [1] and [2]), and how Linux became the
emulators today generate a DELETE when the backspace key is
king, a lot of terminal emulators today generate a DELETE
pressed in order to avoid problems with Linux. The result is
when backspace key is pressed in order to avoid problems
that the only way of generating a BACKSPACE on these systems
with linux. It causes that the only way of generating a
is by using CONTROL + H. (I also think that emacs had an
BACKSPACE in these systems is using CONTROL + H. I also
important point here because the CONTROL + H prefix is used
think that emacs had an important point here because CONTROL
in emacs in some commands (help commands).)
+ 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
connect a real terminal into a machine you describe the type
type of terminal, so getty configure the correct value of
of terminal, so getty configures the correct value of stty
stty erase for this terminal, but in the case of terminal
erase for this terminal. In the case of terminal emulators,
emulators you don't have any getty that can set the correct
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
For this reason, it is necessary to add 'stty erase ^H' to your
backspace keyboard, you have to add a 'stty erase ^H' into
profile if you have changed the value of the backspace key.
your profile. Of course, other solution can be that st
Of course, another solution is for st itself to modify the
itself modify the value of stty erase. I have usually the
value of stty erase. I usually have the inverse problem:
inverse problem, when I connect with non Unix machines, and
when I connect to non-Unix machines, I have to press CONTROL +
I have to press control + h to get a BACKSPACE, or the
h to get a BACKSPACE. The inverse problem occurs when a user
inverse, when a user connects to my unix machines from a
connects to my Unix machines from a different system with a
different system with a correct backspace key.
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
committed by
Roberto E. Vargas Caballero