Which GNOME version and DBUS_SESSION_BUS_ADDRESS for script called from crontab.

[MS <jmstanfield gmail com>]

Hi,

I hope this question is appropriate for this list, there are so many 
GNOME lists. If not please advise me which list I should post it to.

I've written a Bash script for Wallpaper Clocks. The idea of these is to 
build a new wallpaper every minute so that the desktop wallpaper 
displays the current weekday, date, month, hour, and minute. See 
vladstudio.com if the idea appeals.

The script works fine when called from the command line, but it needs to 
be run every minute from crontab to function correctly and this is 
presenting me with 2 related problems, both resulting from crontab not 
logging as your own username, so it doesn't have access to X.

Firstly GNOME v2 and v3 set the wallpaper with different commands; v2 
uses gconftool-2, and v3 uses gsettings. Clearly the script must 
determine which version is running so that the correct command can be 
run. The following command works fine from the command line and outputs 
'2' or '3' but it does not output anything when run from crontab.

gnome-session --version | grep --only-matching '[0-9]*' | head -n 1

Question 1: How do I determine which GNOME version is running from 
within the script when it is run from crontab regardless of which 
flavour of Unix/Linux is running?


Secondly in order to set the wallpaper using gconftool-2 (and I assume 
also with gsettings?, though this is untested at the moment) when the 
script is called from crontab the environment variable 
DBUS_SESSION_BUS_ADDRESS needs to be set.

I have found a method of doing this online, which works with GNOME v2 on 
my Ubuntu desktop (still using Lucid).

It gets the nautilus process ID, then accesses that process's 
/proc/Nautilus_ID/ directory searching the 'environ' file for the 
DBUS_SESSION_BUS_ADDRESS.

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

This does not seem a very elegant solution.

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

Many thanks everyone. Sorry if these are real newbie questions, I'm a 
bit of a GNOME newbie (at least the technical aspects of it, I've been 
running it as my desktop manager for years.)