CODEWITHSUNDEEP
ncursesxtermterminfo
writzlpfrimpft
writzlpfrimpft

Reputation: 371

xterm reports wrong escape sequences on raw input

I am currently trying to do raw input in Linux (e. g. the stuff I'd normally use ncurses or similar).

I already got so far as that every single keypress is directly reported to my application and is dumped as a sequence of hex codes.

If I press the 'a' key on my keyboard, I get this output:

 #  hex string
00 0x61 'a'

This is pretty straight-forward. 0x61 is the hex code for an ASCII 'a' which I can, in turn, print using (char) 0x61 back to the console.

Now I'm trying to do basic line-editing. If I press the left arrow key for example using xterm, I get this output:

 #  hex string
00 0x1B '\x1b'
01 0x5B '['
02 0x44 'D'

According to this website, in the section "Keypad Handling",

The codes sent by the left arrow [...] can be given as kcub1.

According to the termcap file, the sequence should be x1b O D:

 ~ infocmp xterm | grep kcub1
kcub1=\EOD

While this happens in both xterm and termite, it does not in the default tty or urxvt.

According to the xterm faq

escape sequences [...] were chosen as "PC-style" codes (like SCO "ansi"), i.e.,

ESC [ H
ESC [ F

for normal mode, and

ESC O H
ESC O F

for cursor application mode

I guess I have to either set xterm to "normal mode" or replace all O's in the termcap file with "["?

What would be the idial way of reading arrow keys for supporting both xterm & non-xterm terminals?

Then, there's also the cub capability:

cub=\E[%p1%dD

On the same page, there's also a section about "Parameterized Strings". I guess that's what the %p1%d in the cub capability refers to?

%p1 refers to "push first parm", %d refers to "print pop() as in printf".

What does all this mean? What gets pushed to where? I don't call pop() at any point, what does the second option mean?

Thanks for any help in advance.

EDIT: Here is a small C program that demonstrates what I'm talking about. If I compile this using gcc kilo.c and run it, pressing the left arrow key emits 27 91 ('[') 68 ('D'). Note the left bracket instead of the expected O.

Upvotes: 1

Views: 315

Answers (1)

Thomas Dickey
Thomas Dickey

Reputation: 54475

Terminal descriptions' list of special keys are written with the assumption that an application has initialized the terminal for full-screen mode, using application mode for special keys rather than the initial normal mode. Command-line applications generally do not do this (they could, of course: look for smkx and rmkx).

Further reading:

Upvotes: 2

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