bash scripting: random background script for gnome

[carrett]

i'm not a very good scripter, but my friend lent me this script that changes the background to a random image in an image directory. the only trouble is, sometimes it picks up nothing, so the background turns to just colors and no images (what gnome does if it can't find the background image). how do i make it so that it always returns a file in the directory?

here's the script that actually changes the background:

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#!/bin/bash
echo $1
gconftool-2 --type=string --set /desktop/gnome/background/picture_filename "$1"

here's the script that gets a random filename:

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#!/bin/bash

DIRSIZE=`ls $1 | wc -l`

FILENUM=$(($RANDOM % $DIRSIZE))

FILENAME=`ls $1 | head -n $FILENUM | tail -n 1`

#echo $DIRSIZE
#echo $FILENUM
echo $FILENAME

and here's the script that is actually called and ties it all together:

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#!/bin/bash
FILENAME=`/home/carrett/bin/random-filename.sh /home/carrett/img/wall`
echo $FILENAME

#while [$FILENAME==CURRENT_BACKGROUND];
#FILENAME=`/home/carrett/bin/random-filename.sh ~/img/wall`
#echo $FILENAME;


CURRENT_BACKGROUND=$FILENAME

echo $CURRENT_BACKGROUND

/home/carrett/bin/change-background.sh "/home/carrett/img/wall/$FILENAME"

thanks to anyone who actually takes the time to figure this out...driving me nuts!

[royko]

It seems that the problem is this...

To get a random number less than the total number of files in the directory, it does this:

FILENUM=$(($RANDOM % $DIRSIZE))

That takes a random number, divides it by the number of files, and takes the remainder of that division...This is a pretty standard hash trick. It will always give you a number less than the directory size.

Anyway, the problem is that sometimes, the remainder will be zero, and that's when you won't get a file.

If you do something like this right after the line I mentioned:

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if [ "$FILENUM" -eq 0 ]
  FILENUM=1
fi

This should set FILENUM to 1 whenever it's zero.

That should solve the problem, I think.

Also, if you have non-image files in the directory, you may need to filter them out by changing the "ls $1" statements to something like "ls $1/*.jpg", but if you only keep image files in the directory, you shouldn't need to worry about this.

[carrett]

i tried what you said and got this error:

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/home/carrett/bin/random-filename.sh: line 8: syntax error near unexpected token `fi'
/home/carrett/bin/random-filename.sh: line 8: `fi '
 
 
/home/carrett/img/wall/

for reference, here's the only changed script, the one that gets a random filename, in it's full almost-workingness:

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#!/bin/bash

DIRSIZE=`ls $1 | wc -l`

FILENUM=$(($RANDOM % $DIRSIZE))
if [ "$FILENUM" -eq 0 ]
  FILENUM=1
fi 
FILENAME=`ls $1 | head -n $FILENUM | tail -n 1`

#echo $DIRSIZE
#echo $FILENUM
echo $FILENAME

[chris84ae]

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if [ "$FILENUM" -eq 0 ]
then
  FILENUM=1
fi 

wouldnt it be better to add 1 since it is a mod of the number and will therefore never pick the last file

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FILENUM=$(($FILENUM + 1))

[royko]

Sorry, my bad on the syntax...

Yeah, chris, you're right, I didn't think about that. Take out my code and put in his line, so you always add one and never need to test.

I need to make a rule about looking at bash scripts late at night!

[chris84ae]

its 4am over here
this should also work

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FILENUM=$(($RANDOM % $DIRSIZE + 1))

no need to add 1 later on
or shorten everthing to

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#!/bin/bash

FILENUM=$(($RANDOM % `ls $1 | wc -l` + 1))

FILENAME=`ls $1 | head -n $FILENUM | tail -n 1`

[carrett]

this is more of a gnome question than a scripting question, but now my problem is that it doesn't always CHANGE the background, sometimes the random image is the one that's already selected. i've got the while loop i want to have to avoid it, but i don't know how to get the current background...do i use gconftool?

here's the script with the while loop commented out, i need to find some way to get CURRENT_BACKGROUND (the current background).

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#!/bin/bash
FILENAME=`/home/carrett/bin/random-filename.sh /home/carrett/img/wall`
echo $FILENAME

#while [ $FILENAME=CURRENT_BACKGROUND ]; do
#FILENAME=`/home/carrett/bin/random-filename.sh ~/img/wall`
#done
#echo $FILENAME


CURRENT_BACKGROUND=$FILENAME

echo $CURRENT_BACKGROUND

/home/carrett/bin/change-background.sh "/home/carrett/img/wall/$FILENAME"

[royko]

Well, I don''t know about gnome, but since you're using a script to set the background, why not just write the filename to a file when you do the setting, so that you can just read that filename from the file later?

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echo "CURRENT_BACKGROUND=$FILENAME" > currentbg

Then later, to retrieve it, just add

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. currentbg

[carrett]

ok, here's the complete working scripts for anyone who cares:

~/bin/change-background.sh

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#!/bin/bash
echo $1
gconftool-2 --type=string --set /desktop/gnome/background/picture_filename "$1"

~/bin/random-filename.sh

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#!/bin/bash
 
DIRSIZE=`ls $1 | wc -l`
 
FILENUM=$(($RANDOM % `ls $1 | wc -l` + 1))
 
FILENAME=`ls $1 | head -n $FILENUM | tail -n 1`
 
#echo $DIRSIZE
#echo $FILENUM
echo $FILENAME

~/bin/random-background.sh

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#!/bin/bash
FILENAME=`/home/carrett/bin/random-filename.sh /home/carrett/img/wall`
 
until [ $FILENAME != $(cat ~/bin/cbg) ]; do
FILENAME=`~/bin/random-filename.sh ~/img/wall`
done
 
CURRENT_BACKGROUND=$FILENAME
 
echo $CURRENT_BACKGROUND > ~/bin/cbg
 
/home/carrett/bin/change-background.sh "/home/carrett/img/wall/$FILENAME"

of course replace all /home/carrett occurrences with whatever your home directory and chmod +x all the scripts. to have it done every hour, set up a cron job, here's the relevant part of my /etc/crontab:

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0 *  * * *	carrett	/home/carrett/bin/random-background.sh

finally, to avoid the stupid annoying sendmail messages without getting postfix (or something like it) i've found the best thing to do is replace /sbin/sendmail with a chmod +x'ed script that directs all input to /dev/null, like this (not my idea):

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#!/bin/bash
echo ${*} > /dev/null
exit 0

I hope people find this helpful. Most of these ideas (including the original scripts) aren't mine, so thanks to everyone. later.

[credmp]

Hi,

of course replace all /home/carrett occurrences with whatever your home directory and chmod +x all the scripts. to have it done every hour, set up a cron job, here's the relevant part of my /etc/crontab:

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0 *  * * *	carrett	/home/carrett/bin/random-background.sh

To prevent messages from being mailed to you (which happens if the script produces output) you can just redirect the output of the script to /dev/null like so;

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0 *  * * *	carrett	/home/carrett/bin/random-background.sh 2>&1 > /dev/null

regards

EDIT: fixed the redirect... forgot the > (kinda important

[carrett]

i'd seen something like that before as a solution to the constant email problem. i tried it...but i still got the

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sendmail: could not open mailserver:25

error clogging up my console. so...i still say my best bet is to make /usr/sbin/sendmail an execuatble script that directs everything sent to it to /dev/null. if anyone has dealt with this in a way that can be solved simply by editing crontab, i'm willing to try your solution, so far this is the only one that works though..

[credmp]

i'd seen something like that before as a solution to the constant email problem. i tried it...but i still got the

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sendmail: could not open mailserver:25

error clogging up my console. so...i still say my best bet is to make /usr/sbin/sendmail an execuatble script that directs everything sent to it to /dev/null. if anyone has dealt with this in a way that can be solved simply by editing crontab, i'm willing to try your solution, so far this is the only one that works though..

The cron manpage says

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any  output  is  mailed  to  the owner  of  the  crontab (or to the user named in the MAILTO environment variable in the crontab, if such exists).

So per definition redirecting output to /dev/null gets rid of the mailing... give it a try and see

regards

[carrett]

i'm saying i did try and it didn't work.

[razamatan]

i wrote my own method for doing this... it does all the errors that could possibly arise (and ignores the ones that don't matter, like args > 2).

name this script "rl" and put it in your path:

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#!/usr/bin/perl
# rl: randomizes lines
$i=@a=<>;while($i--){$j=int(rand($i+1));@a[$i,$j]=@a[$j,$i]}print@a

the script above is quite handy... very multi-purpose. it randomizes anything. it can handle filenames as args, or lines via standard input... perl magic.

name this script whatever you want to and put it in your path:

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#!/bin/sh
# changes the background randomly
 
opts="wallpaper centered scaled stretched"
exts="\.(jpg|jpeg|gif|bmp|png)$"
 
filekey="/desktop/gnome/background/picture_filename"
optkey="/desktop/gnome/background/picture_options"
 
if [ $# == 0 ] ; then
   echo "usage: `basename $0` directory|file [option]"
   echo "the directory|file must be ~/path or /path/stuff"
   exit 1
fi
 
opt="scaled"
if [ ! -z $2 ] ; then
   echo $opts | grep -q "${2}\b"
   if [ $? == 0 ] ; then opt=$2
   else echo "invalid option: defaulting to scaled" ; fi
fi
 
file=$1
if [ -d $1 ] ; then
   file=$(find $1 -type f | grep -Ei "$exts" | rl | head -1;)
   until [ "$file" != "$(gconftool-2 -g $filekey)" ] ; do
      file=$(find $1 -type f | grep -Ei "$exts" | rl | head -1;)
   done
fi
 
# to prevent relative paths
cd /
 
if [ ! -z "$file" ] && [ -f "$file" ] ; then
   gconftool-2 -t string -s $filekey "$file" -s $optkey $opt
else echo unable to retrieve image ; exit 1
fi

i have this script called "chbkg". very cron-able...

[razamatan]

i got bored, and i made a perl version of the 2nd script... i think it handles things a tad better... i think..

you still need the rl script... it's a handy script to have neway...

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#!/usr/bin/perl
# changes the background randomly
use strict;
                                                                                
die "usage: $0 directory|file [option]\nthe directory|file must be ~/path or /path/stuff\n" if ($#ARGV < 0 || $#ARGV > 2);
                                                                                
my $opts = 'wallpaper|centered|scaled|stretched';
my $exts = 'jpg|jpeg|gif|bmp|png';
                                                                                
my $filekey = "/desktop/gnome/background/picture_filename";
my $optkey = "/desktop/gnome/background/picture_options";
                                                                                
my $file = shift(@ARGV);
if (-d $file) {
   foreach (`find $file -type f | grep -Ei \"\\\.($exts)\$\" | rl`) {
      $file = $_;
      last if ($file ne `gconftool-2 -g $filekey`);
   }
}
                                                                                
my $opt = shift(@ARGV);
unless ($opt && $opt =~ /^($opts)$/i) { $opt = "scaled"; }
                                                                                
chomp($file);
if (-f "\/$file") {
   system "gconftool-2 -t string -s $filekey \"$file\" -s $optkey $opt"
} else { die "unable to retrieve image\n"; }

yeah.. i should be studying for my exams...

[carrett]

doh! the problem was that it wasn't emailing, it was just putting errors onto the console. anyway, i started using exim and the problems have ceased somewhat.