Shell Programming and Scripting

Hi,

I'm writing a Bash script for wallpaper clocks which works fine on the command line but needs to be run every minute from a crontab entry so the time gets changed on the wallpaper (the wallpaper gets rebuilt every minute so the current weekday, date, month, hour, and minute become part of the wallpaper).

The script changes the wallpaper like this, depending on which version of Gnome is running:

Code:

Gnome v.2:
gconftool-2 -t string -s /desktop/gnome/background/picture_filename "$currentImagePath"

Gnome v.3:
gsettings set org.gnome.desktop.background picture-uri "file://$currentImagePath"

The change wallpaper commands above run fine from the command line but when the script is run from crontab it seems the DBUS_SESSION_BUS_ADDRESS environment variable must be set otherwise the wallpaper does not get changed (although all other aspects of the script work fine).

Is there a generic way to get and set the value of DBUS_SESSION_BUS_ADDRESS from within the script which will work with both Gnome v.2 and v.3 and regardless of which flavour of Unix/Linux is running?

I've found 2 methods on the web:

Code:

nautilus_pid=$(pgrep -u $LOGNAME -n nautilus)
eval $(tr '\0' '\n' < /proc/$nautilus_pid/environ | grep '^DBUS_SESSION_BUS_ADDRESS=')
export DBUS_SESSION_BUS_ADDRESS

Code:

export `grep ^DBUS_SESSION_BUS_ADDRESS \
$HOME/.dbus/session-bus/$(dbus-uuidgen --get)-$(echo $DISPLAY \
| sed -e 's/\([^:]*:\)//g' -e 's/\..*$//g')`

I must say that both methods seem very inelegant! And I only know that they work on my Linux desktop which runs Ubuntu with Gnome v.2. Is there a better generic and reliable way to get and set the value of DBUS_SESSION_BUS_ADDRESS from a script called from crontab? If so, then how?

Finally, could some kind soul explain to me why I need set the DBUS_SESSION_BUS_ADDRESS so that the wallpaper will successfully be changed when running the script from crontab, while it is unnecessary when running the same script from the command line?

Many thanks all.

crontab doesn't login as you, so it doesn't get access to X.

Some of those things seem unavoidable, like the uidgen --get. Others, like the echo $DISPLAY | sed 'enormous ugly regex', can probably be made less ugly. And the eval almost certainly isn't necessary.

Without seeing what it's actually doing, of course, what those commands output and its end result, I can't rewrite it.

Thanks Corona.

Ok, got it.

In the absence of any other ways of doing it (anyone?), which would you think was most likely to work with different flavours of Unix/Linux and Gnome v.2 or 3? Or do you think both will work regardless of Unix/Linux and Gnome version?

Extremely difficult to say. dbus is a completely generic thing that can be used in a multitude of ways. Guaranteeing later versions of Gnome would work the same way because they use dbus would be like guaranteeing later versions of Gnome work the same way because they use files...

Ok thanks again for the help.

Anyone else got further info. on this?

Cheers all.