[TUHS] Literal character escapes in v7

[will.senn@gmail.com (Will Senn)]

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On 11/7/17 3:07 AM, Dennis Boone wrote:
>   > I'm not looking for code review, but the code is intended to replace
>   > the tabs and backspaces with \t and \b respectively, but I haven't
>   > been able to test it because I can't seem to make a backspace
>   > character appear in input. In later unices, ^V followed by the
>   > backspace would work, but that's not part of v7. Backspace itself is
>   > my erase character, so anytime I just type it, it backspaces :).
>
> This bit from the middle of sys/dev/tty.c seems to indicate that you
> escape it with \:
>
> 	} else {
> 		mc = maptab[c];
> 		if (c==tp->t_erase || c==tp->t_kill)
> 			mc = c;
> 		if (mc && (mc==c || (tp->t_flags&LCASE))) {
> 			if (bp[-2] != '\\')
> 			c = mc;
> 			bp--;
> 		}
> 	}
>
> On my test v7 system if I type backslash control-h:
>
> 	# stty
> 	speed 0 baud
> 	erase = '^H'; kill = '^U'
> 	even -nl echo -tabs
> 	# echo \^H | od -c
> 	0000000  \b  \n
> 	0000002
> 	#
>
> De

Thanks for the note. I thought about it and tried it out even though I 
don't see the ^H (my cursor backs up a space).

After typing echo "\^H" | od -c, here's what it looks like:

$ echo "" | od -c
0000000  \b  \n
0000002

So, sure enough there's a backspace in there and my code "sees" it too:

$ echo "" | 1-8
<<BACKSPACE>>
$


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