Hi Tim,
> I sometimes think the same about the default tty signal mapping of
> Ctrl-\ for SIGQUIT -- the two keys appear next to either other on this
> keyboard, so is easy for e.g. a cat to type (or even a mis-typed
> Ctrl-Z undo attempt).
I typed this TTY's QUIT character on Wednesday by accident. Here, it's
also defined as Ctrl-\. But I typed Ctrl-Shift-4; I probably wanted ‘$’
but Ctrl was still on its way up.
Actually, the Shift isn't required; Ctrl-4 does SIGQUIT too, and not
because of the bit-twiddling reason that Ctrl-2 gives NUL just as Ctrl-@
should: that Shift-2 is ‘"’. xterm's input.c says it's an X thing, but
I haven't found anything else about it:
* X "normally" has some built-in translations, which the user may want to
* suppress when processing the modifyOtherKeys resource. In particular,
the
* control modifier applied to some of the keyboard digits gives results for
* control characters.
Here's me entering Ctrl-1, Ctrl-2, ... up to Ctrl-0 and then Enter.
$ stty raw; \
> ((timeout --foreground 4.2 dd bs=1; stty cooked; echo >&3) | hd) 3>&1
1^@^[^\^]^^^_^?9^M
00000000 31 00 1b 1c 1d 1e 1f 7f 39 0d |1.......9.|
0000000a
$
You can see the TTY's ‘ctlecho’ setting causing Ctrl-2 to be echoed as
‘^@’, NUL, and that's confirmed by the hex dump. 0x1c is backslash,
0x5c, with Ctrl masking off 0x40.
--
Cheers, Ralph.
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