Bash in gnome-terminal shows control characters as unsupported-unicode squares

Reported by Quintin Beukes on 2009-12-30
This bug affects 5 people
Affects Status Importance Assigned to Milestone
gnome-terminal (Ubuntu)
Ubuntu Desktop Bugs

Bug Description

Binary package hint: gnome-terminal

When I upgraded to Karmic (clean install) I noticed bash echoes control characters using the hat notation (ex. ctrl+c shows as ^C). stty reported echoctl being set, so I tried to unset it. This helped, and pressing ctrl+c at a prompt cancels the prompt, shows a new one and nothing is echoed.

Though, when pressing ctrl+c while a program is running (ex. cat or ping), a unicode square is echoed like for unicode characters not supported by the selected font. I tried selecting many different encodings and fonts, though nothing seemed to help.

Futher, if inside this same shell I open a screen session, this behaviour is gone and everything works as intended, which is to have ctrl+c or ctrl+z have the desired effect with nothing echoed.

Finally, opening a bash session in xterm or tty[1-6] and disabling echoctl/ctrlecho using stty command, this cannot be reproduced. So it seems that only an plain bash session in gnome-terminal does this.

To see a screenshot, view the attached PNG.
Basically what happens there is
1. 2 ctrl+c presses at the prompt.
2. Then 1 ctrl+c during cat
3. Then 1 ctrl+z during cat
4. Bring cat back to the foreground and press ctrl+c again
THEN disable echoctl
5. Repeat the process - where you can now see instead of hat notation, the prompt presses are fine, but the in-program presses echo unicode squares.

Very frustrating.

ProblemType: Bug
Architecture: i386
Date: Wed Dec 30 12:40:10 2009
DistroRelease: Ubuntu 9.10
ExecutablePath: /usr/bin/gnome-terminal
InstallationMedia: Ubuntu 9.10 "Karmic Koala" - Release i386 (20091028.5)
NonfreeKernelModules: fglrx
Package: gnome-terminal 2.28.1-0ubuntu1
 PATH=(custom, no user)
ProcVersionSignature: Ubuntu 2.6.31-16.53-generic
SourcePackage: gnome-terminal
Uname: Linux 2.6.31-16-generic i686

Quintin Beukes (quintin) wrote :
Pedro Villavicencio (pedro) wrote :

do you get the same with terminator(terminal emulator) or xterm?

Changed in gnome-terminal (Ubuntu):
assignee: nobody → Ubuntu Desktop Bugs (desktop-bugs)
importance: Undecided → Low
status: New → Incomplete
Quintin Beukes (quintin) wrote :

Can be reproduced with:
gnome-terminal: YES
terminator: YES
xterm: NO
tty[1-6]: NO

I attached another screenshot showing a ctrl+c in "/bin/cat" for gnome-terminal, terminator and xterm.

Quintin Beukes (quintin) wrote :

An easy way to reproduce this is to just do:
printf "\003\n\x1A\n"

This shows than when receiving these characters, gnome-terminal tries to print them, instead of ignoring them.

When doing: printf "##\003##\n", gnome-terminal (and thus also terminator), will print 2 hash characters, then the unicode square, then another hash covering the 2nd half of the unicode square (because the square is seen as a single character, though it takes up the space for 2), then another hash.

Xterm, screen and tty (TERM==linux) the same command will just print 4 hash characters.

If this might help, I have to mention again that running a screen session in gnome-terminal it works as intended. I don't know if this is the doing of ncurses or a terminfo configuration, or the separate utf8 encodings installed with screen.

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