From: Erland Sommarskog (sommar-usefor@algonet.se)
Date: Sat Jan 05 2002 - 14:57:53 CST
Charles Lindsey (chl@clw.cs.man.ac.uk) writes:
> In <20011229212634.19181.qmail@wilhelmina.algonet.se> sommar-usefor@algonet.se (Erland Sommarskog) writes:
> >Some Telnet clients or terminals could start to act funny if fed a
> >CSI and they are set to accept 8-bit controls.
>
> But are there any legitimate and defined uses for those 8 bit control
> characters of ISO 8859? Do those Telnet clients or terminals actually take
> special note of them (other than not displaying them)? If not, no problem
> arises. Note that the control characters in the ASCII range are not a
> problem, since they do not occur in UTF-8 except as themselves.
CSI (Control Sequence Introducer) is 7-bit parlance ESC-[, but with
8-bit controls is character 155 (128 + 27). CSI is used for a lot
things. CSI - A is Cursor Up.
I look in a VT320 manual that I have dearly kept through the years,
and the following 8-bit control characters are recognized: IND, NEL,
HTS, RI, SS2, SS3, DCS, CSI, ST, OSC, PM and APC. The latter three
are particuarly cute: VT320 ignores all subsequent characters until
it receives an ST character.
All these have seven-bit equivalents, On a VT320 you can select whether
you want 7-bit and 8-bit controls, and in the manual Digital recommends
7-bit controls.
Not very many are using VT320 these days, but Telnet and SSH clients
are less rare. I played some games with my SSH client, and inserted
CSI-A in a file, and indeed, the cursor went up one line. I also
tried APC, but the text was not swallowed as advertised. Then again,
SecureCRT only offers VT220 emulation, so it could be that APC was
added to VT320.
So users of VT220 emulating clients, could run into surprises with
UTF-8 names for non-Western scripts. Then again, they are just as
much in danger when viewing messages in Windows-1252. (155 is defined
in this charset as SINGLE RIGHT-POINTING ANGLE QUOTATION MARK, U+203A.)
-- Erland Sommarskog, Stockholm, sommar@algonet.se