Here is how to add a custom script in Unity HUD/dash for quick access. /usr/share/applications directory has all shortcuts for Unity desktop. So create a file named “mycustomscript.desktop” (or any_name_you_like.desktop) there which has information about the custom script. Additionally an icon could be added by pointing to an image. Files in /usr/share/applications directory have to be created as root.
[Desktop Entry] Version=1.0 Type=Application Terminal=false StartupNotify=true Icon=/home/vishalj/Pictures/mycustomscript.jpeg Name=MyCustomScript Comment=My Custom Script for X, Y and Z Exec=/home/vishalj/scripts/mycustomscript.sh Categories=Application;Productivity
sudo update-desktop-database after which you will be able to use Unity HUD for invoking the custom script. Also note that each time you update a .desktop file you have to run