I decided to go ahead and write the code to allow Zenity to listen for commands on stdin. It was pretty easy to add, and Glynn accepted the patch so it is in the latest CVS version. The main difference between the implementation and what I described earlier is that you need to pass the --listen argument to Zenity to activate this mode (without it, it acts as a one-shot notification icon where it exits when the icon is clicked on). The easiest way to use it from a bash script is to tie Zenity to a file descriptor like this:
exec 3> >(zenity --notification --listen)
You can then feed commands to the notification icon by echoing things to that file descriptor. For example:
echo "tooltip: a new tooltip" >&3
The available commands are icon, tooltip and visible. When you’ve finished and want to kill off the icon, you can simply close the file descriptor:
Some things that would be good to add are message balloon support (although the Gnome system tray doesn’t seem to support them right now) and support for animated images (useful to get the user’s attention while message balloons don’t work).
One of the reasons for adding this functionality to Zenity was for use in jhbuild. Davyd did the initial prototype for this, but the idea for the notification icon seemed fairly generic and useful outside of jhbuild. Also, by putting it in Zenity there is less to maintain in jhbuild itself