Unity: how to add a shell-script to the dock

You need to make a shortcut-file. Shortcuts for the Unity dock are located in ~/.local/share/applications/

1. Create a file myGUIapp.desktop in that directory.

2. Paste the following into that file (with correct paths for icon and shellscript):

   [Desktop Entry]
   Name=My GUI App
   Exec=/path/to/shellscript.sh
   Icon=/path/to/you/icon.svg
   Terminal=false
   Type=Application
   StartupNotify=true
   

3. Make the file executable:

   Right click -> Properties -> Permissions -> Tick ‘Allow executing as a program’

4. Restart Unity (or drag the file to the Dock to get it there directly).

Look in other files in ~/.local/share/applications/ to get an idea of how they should look. More info is available in this blog entry.

Edit:
If you want the shortcut to be accessable to all users you should check out Ubuntu packaging guide about icons.
Basically the .desktop-file are installed or moved to /usr/share/applications/<binary>.desktop instead and icons are placed in /usr/share/icons/hicolor/scalable/apps