Indicator System Monitor

The closest method I’ve found to satisfy your requirements is (webupd8.org - Ubuntu appindicator that displays bash) that displays text on the Unity system tray / application indicator bar. The sample above comes from two bash scripts: multi-timer and display-auto-brightness.

Install and Configure Sysmonitor Indicator

You need to install indicator-sysmonitor from ppa:

sudo add-apt-repository ppa:fossfreedom/indicator-sysmonitor
sudo apt-get update
sudo apt-get install indicator-sysmonitor

Then run the gui and configure it with the script name that updates the system tray.

Here are a few examples from the WebUpd8 link above:

`echo $(grep "cpu MHz" /proc/cpuinfo | head -1 | cut -d ' ' -f3 | cut -d '.' -f1) MHz`

`if wget -O /dev/null webupd8.org > /dev/null; then echo "☺"; else echo "☹"; fi`