Ctrl-N sequences (was: Re: Console codepage setting via chcp?)

[Andy Koppe <andy dot koppe at gmail dot com>]

2009/9/26 Corinna Vinschen:
> The \016\377\x is the multibyte
> sequence which gets created from a lone U+DCxx UTF-16 value in
> sys_cp_wcstombs.

Forgot to say: that makes sense.

Which reminds me, regarding ^N sequences I stumbled across the following issue.

^N switches vt100-compatible terminals to the so-called G1 character
set, away from the default G0. ^O switches back. G0 and G1 can
independently be mapped to ASCII, linedraw or VGA (as well as various
obsolete ASCII variations). Different escape sequences are needed to
configure G0 and G1. (vt220 adds G2 and G3, for more such fun.)

Hence the problem with ^N being displayed as part of a filename is
that the normally used G0 sequences for switching to the linedraw or
VGA character sets will no longer appear to work afterwards, since G1
is active. Less likely, if G1 happens to be set to the linedraw
charset, a ^N will turn all lowercase characters into hieroglyphics.
(I did experience that effect because the xgraphics test file I'd
attached had switched G1 to the linedraw charset.)

Therefore, is there a particular reason for choosing ^N, or could it
be changed to a control character that does not have a special meaning
to terminals? The following are taken:

^E ^G ^H ^I ^J ^K ^L ^M ^N ^O ^[

And these ones are usually taken by the pty (although they're less of
an issue, as they're special only on input rather than output):

^C ^D ^Q ^R ^S ^U ^V ^W ^Z ^\

Anyway, this leaves:

^A ^B ^F ^P ^T ^X ^Y ^] ^^ ^_

All of which mean something or other to readline, but again, they're
only special on keyboard input, not on output to the terminal screen.

How about ^X? Somewhat mnemonic, because Alt+X allows entering Unicode
codepoints in many Windows apps.

Andy