[SOLVED] bash scripting, xrandr, and grep

comp_brad1136 · 03-06-2011, 01:30 PM

There may be a much better why to do what I'm trying to do.

In the windoze world, if your plug your monitor into your laptop, the display magically jumps over to it. Unplug your monitor, and it's back to your laptop.

I've tried many things to do that using debian squeeze, but can't get it.

In high spirits, i decided to be a good little linux user and make a simple script. I thought.

Code:

#/bin/bash
if [ "$(xrandr -q) | $(grep 'VGA1 disconnected')" ]
then
echo "disconnected"
fi

This doesn't do anything at all. I have to C-c to end the script.
The ultimate goal is to make it so I can run the same script to set the monitor resolution or turn my lcd back on.

This is what I have in mind, written in C-ish style:

Code:

if ( $(xrandr -q) | $(grep 'VGA1 connected') )
   { $(xrandr --output VGA1 --mode 1280x1024 --output LVDS1 --off);}
else
   { $(xrandr --output VGA1 off --output LVDS1 --mode 1024x600); }

dont make too much fun of the C, i know it's not at all valid, but it makes a valid illustration!

corp769 · 03-06-2011, 01:47 PM

I would put the output of xrandr -q into a variable, along with the grep, like so:

Code:

var1=`xrandr -q | grep 'VGA1 disconnected'`

comp_brad1136 · 03-06-2011, 02:28 PM

Code:

#/bin/bash
noMonitor=`xrandr -q | grep 'VGA1 disconnected'`
if [ $noMonitor ]
then
xrandr --output VGA1 --off --output LVDS1 --mode 1024x600
else
xrandr --output VGA1 --mode 1280x1024 --output LVDS1 --off
fi

produces

[: 8: VGA1: unexpected operator

corp769 · 03-06-2011, 02:31 PM

Code:

if [ -z "$noMonitor" ];

The -z test if $var1 is set or unset.

comp_brad1136 · 03-06-2011, 09:48 PM

i still have some complaining about unexpected operator VGA1 when monitor is disconnected. However, it does perform it's purpose.

Code:

#/bin/bash
Monitor=`xrandr -q | grep 'VGA1 disconnected'`
if  [ -z  $Monitor ]
then
echo Monitor detected.
$(xrandr --output VGA1 --mode 1280x1024 --output LVDS1 --off)
return 0
else
echo No monitor detected.
$(xrandr --output VGA1 --off --output LVDS1 --mode 1024x600)
return 0
fi

i think I'm going to do it in C, just for grins. If there is any ideas on why it still complains when monitor is disconnected, let me know!

I'll post the C code, just for viewing pleasure

comp_brad1136 · 03-06-2011, 11:16 PM

Code:

#include <cstdlib>

int main(){
        using namespace std;
        bool bMonitor = system("xrandr -q | grep 'VGA1 disconnected'");
        if ( bMonitor ){
                system("xrandr --output VGA1 --mode 1280x1024 --output LVDS1 --off");
        }
        else{
                system("xrandr --output VGA1 --off --output LVDS1 --mode 1024x600");
        }

        return 0;
}

I dont know if I should be proud, ashamed, or annoyed. This took just a minute, and works perfectly.

What kind of idiot can write a cpp to do this, but cant get a bash script to do it? All well!

Note to viewers: this program does raise security issues, because it assumes xrandr and screen have not been compromised. If anybody wants this for their system, let me know and I'll add a little more to it to make it safer.

David the H. · 03-06-2011, 11:32 PM

You may be going about it the wrong way. I suggest looking into halevt, which uses hal to search for specified system events such as adding and removing hardware and runs arbitrary commands when it detects them.

comp_brad1136 · 03-07-2011, 07:47 AM

i ran $ halevt -i to see what happens. It performs as advertised when i unplugged my mouse and plugged it back in. But, it didn't do that with my monitor. It's a nifty daemon though, and I won't forget it's existance. Thank you for the suggestion!