Add info about Backspace and Delete to the FAQ
Here is a modest attempt at cleaning it up a little bit. I changed a few phrases that seemed awkward, but I think the content is the same. -- Wolfgang Corcoran-Mathe Signed-off-by: Roberto E. Vargas Caballero <k0ga@shike2.com>
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FAQ
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FAQ
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@ -104,54 +104,53 @@ This is an issue that was discussed in suckless mailing list
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<http://lists.suckless.org/dev/1404/20697.html>:
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<http://lists.suckless.org/dev/1404/20697.html>:
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Well, I am going to comment why I want to change the behaviour
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Well, I am going to comment why I want to change the behaviour
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of this key. When ascii was defined in 1968 communication
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of this key. When ASCII was defined in 1968, communication
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with computers were done using punched cards, or hardcopy
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with computers was done using punched cards, or hardcopy
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terminals (basically a typewritter machine connected with
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terminals (basically a typewriter machine connected with the
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the computer using a serial port). Due to this, ascii defines
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computer using a serial port). ASCII defines DELETE as 7F,
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DELETE as 7F, because in the puched cards, it means all the
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because, in punched-card terms, it means all the holes of the
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holes of the card punched, so it is a kind of 'phisical
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card punched; it is thus a kind of 'physical delete'. In the
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delete'. In the same way, BACKSPACE key was a non destructive
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same way, the BACKSPACE key was a non-destructive backspace,
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back space, as in typewriter machines. So, if you wanted
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as on a typewriter. So, if you wanted to delete a character,
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to delete a character, you had to BACKSPACE and then DELETE.
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you had to BACKSPACE and then DELETE. Another use of BACKSPACE
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Other use of BACKSPACE was accented characters, for example
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was to type accented characters, for example 'a BACKSPACE `'.
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'a BACKSPACE `'. The VT100 had no BACKSPACE key, it was
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The VT100 had no BACKSPACE key; it was generated using the
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generated using the CONTROL key as another control character
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CONTROL key as another control character (CONTROL key sets to
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(CONTROL key sets to 0 b7 b6 b5, so it converts H (code
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0 b7 b6 b5, so it converts H (code 0x48) into BACKSPACE (code
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0x48) into BACKSPACE (code 0x08)), but it had a DELETE key
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0x08)), but it had a DELETE key in a similar position where
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in a similar position where BACKSPACE key is located today
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the BACKSPACE key is located today on common PC keyboards.
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in common PC keyboards. All the terminal emulators emulated
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All the terminal emulators emulated the difference between
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correctly the difference between these keys, and backspace
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these keys correctly: the backspace key generated a BACKSPACE
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key generated a BACKSPACE (^H) and delete key generated a
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(^H) and delete key generated a DELETE (^?).
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DELETE (^?).
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But the problem arised when Linus Torvald wrote Linux, and
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But a problem arose when Linus Torvalds wrote Linux. Unlike
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he did that the virtual terminal (the terminal emulator
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earlier terminals, the Linux virtual terminal (the terminal
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integrated in the kernel) returns a DELETE when backspace
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emulator integrated in the kernel) returned a DELETE when
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was pressed, due to the fact of the key in that position
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backspace was pressed, due to the VT100 having a DELETE key in
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in VT100 was a delete key. This created a lot of problems
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the same position. This created a lot of problems (see [1]
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(you can see it in [1] and [2]), and how Linux became the
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and [2]). Since Linux has become the king, a lot of terminal
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king, a lot of terminal emulators today generate a DELETE
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emulators today generate a DELETE when the backspace key is
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when backspace key is pressed in order to avoid problems
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pressed in order to avoid problems with Linux. The result is
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with linux. It causes that the only way of generating a
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that the only way of generating a BACKSPACE on these systems
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BACKSPACE in these systems is using CONTROL + H. I also
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is by using CONTROL + H. (I also think that emacs had an
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think that emacs had an important point here because CONTROL
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important point here because the CONTROL + H prefix is used
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+ H prefix is used in emacs in some commands (help commands).
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in emacs in some commands (help commands).)
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From point of view of the kernel, you can change the key
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From point of view of the kernel, you can change the key
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for deleting a previous character with stty erase. When you
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for deleting a previous character with stty erase. When you
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connect a real terminal into a machine you describe the
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connect a real terminal into a machine you describe the type
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type of terminal, so getty configure the correct value of
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of terminal, so getty configures the correct value of stty
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stty erase for this terminal, but in the case of terminal
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erase for this terminal. In the case of terminal emulators,
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emulators you don't have any getty that can set the correct
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however, you don't have any getty that can set the correct
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value of stty erase, so you always get the default value.
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value of stty erase, so you always get the default value.
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So it means that in case of changing the value of the
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For this reason, it is necessary to add 'stty erase ^H' to your
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backspace keyboard, you have to add a 'stty erase ^H' into
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profile if you have changed the value of the backspace key.
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your profile. Of course, other solution can be that st
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Of course, another solution is for st itself to modify the
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itself modify the value of stty erase. I have usually the
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value of stty erase. I usually have the inverse problem:
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inverse problem, when I connect with non Unix machines, and
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when I connect to non-Unix machines, I have to press CONTROL +
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I have to press control + h to get a BACKSPACE, or the
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h to get a BACKSPACE. The inverse problem occurs when a user
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inverse, when a user connects to my unix machines from a
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connects to my Unix machines from a different system with a
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different system with a correct backspace key.
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correct backspace key.
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[1] http://www.ibb.net/~anne/keyboard.html
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[1] http://www.ibb.net/~anne/keyboard.html
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[2] http://www.tldp.org/HOWTO/Keyboard-and-Console-HOWTO-5.html
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[2] http://www.tldp.org/HOWTO/Keyboard-and-Console-HOWTO-5.html
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