Keyboard special keys

ychaouche · 12-06-2023, 08:15 AM

Dear LQ,

I was just curious to know if any of you had any bindings for the following keys:
- Sys Rq
- Pause/break
- Scroll Lock

I'd like to use one of these keys in my inputrc to start capturing output from the terminal in a tmp file.
Another keypress on same key would toggle the function off.
I'd also like to use a second key combination to paste the content of last command directly in the command line (more here).

I just wanted to make sure that it was ok to bind these keys,
and also curious if anyone had any special keybindings already bound to them.

hazel · 12-06-2023, 08:20 AM

SysReq does. I have never actually got this thing to work, but apparently you are supposed to be able to get out of keyboard freezes by holding down SysReq and typing reisub.

ychaouche · 12-06-2023, 10:58 AM

Ok so here's code to capture output of last command.
The idea is to press C-x C-: to start capturing output,
then issue any command.
You can put the last line of output of that command to the clipboard with C-x C-x,
or paste it to the terminal with C-x C-v.

The only thing that doesn't work is toggling output capture with C-x C-:
I can't seem to use that key combination.
Anyone has an idea?
see code below

Code:

export CAPTUREOUTPUT=-1

sys.capture.output.on(){
    exec > >(tee -a /tmp/output)
    CAPTUREOUTPUT=0
    debug "capture is on"
}

sys.capture.output.off(){
    exec > /dev/tty
    CAPTUREOUTPUT=-1
    debug "capture is off"    
}

sys.capture.output.toggle(){
    if (( $CAPTUREOUTPUT == 0 ))
    then
	debug "turning off output capture"
	sys.capture.output.off
    else
	debug "turning on output capture"
	sys.capture.output.on
    fi
}

sys.capture.output.last(){
    n=${1:-1}
    tail -n"$n" /tmp/output
}

sys.capture.output.last.copy(){
    desktop.clipboard.set "$(sys.capture.output.last)"
}


debug(){
    echo $@ > /dev/stderr
}

sys.capture.output.last.paste(){
    READLINE_LINE="$READLINE_LINE$(sys.capture.output.last)";
    READLINE_POINT=${#READLINE_LINE}
}

bind -x '"\C-x\C-v": sys.capture.output.last.paste'
bind -x '"\C-x\C-x": sys.capture.output.last.copy'
bind -x '"\C-x\C-:": sys.capture.output.toggle'

DavidMcCann · 12-06-2023, 11:23 AM

Quote:

Originally Posted by hazel

I have never actually got this thing to work, but apparently you are supposed to be able to get out of keyboard freezes by holding down SysReq and typing reisub.

You hold down both Alt and SysReq, release SysReq, and then type REISUB for reboot ot REISUO to shut down. Don't press the keys too quickly — each step obviously has to complete before the next one.

If the facility is set, the you should get the reply "1" from

Code:

 cat /proc/sys/kernel/sysrq

If you don't, use

Code:

echo "1" >/proc/sys/kernel/sysrq

ychaouche · 12-06-2023, 11:34 AM

Quote:

Originally Posted by ychaouche

The only thing that doesn't work is toggling output capture with C-x C-:

For some reason it has to be C-x: instead of C-xC-:.
*It* doesn't tell the difference between the two,
whatever *it* is.

For the complete solution see my updated answer on SO.

lvm_ · 12-06-2023, 11:48 AM

Quote:

Originally Posted by ychaouche

I was just curious to know if any of you had any bindings for the following keys:
- Sys Rq
- Pause/break
- Scroll Lock

ScrollLock is one of keyboard layout switching keys for multilingual environments (setxkbmap -option grp:sclk_toggle), and ScrollLock LED can be set up to to indicate the current layout (grp_led:scroll). I always set it up this way.

Quote:

Originally Posted by DavidMcCann

You hold down both Alt and SysReq, release SysReq, and then type REISUB for reboot ot REISUO to shut down.

Actually it's way more complex and flexible than that: https://www.kernel.org/doc/html/late...ide/sysrq.html

hazel · 12-07-2023, 12:06 AM

Quote:

Originally Posted by DavidMcCann

You hold down both Alt and SysReq, release SysReq, and then type REISUB for reboot ot REISUO to shut down. Don't press the keys too quickly — each step obviously has to complete before the next one.

Ah, that explains it! I thought you had to keep the alt+sysReq keys down throughout the sequence. Thanks a lot!

ychaouche · 12-07-2023, 02:12 AM

It used to work for me for years until I changed my keyboard -_-
The old keyboard had a clear label on the sysrq key,
but not this one,
so I can't tell which one it is.
Thanks to the kernel.org link,
now I know it's the same as the Print Screen key.