gnome-screenshot copy to clipboard shortcut
There are a set of keyboard shortcuts in Ubuntu specifically for screenshots.
Go to System Settings > Keyboard > Shortcuts > Screenshots. In my case it is Ctrl+Shift+Print_Screen
I found out the solution.
First, open the shortcut dialog window and press add
to add a new shortcut. Then paste this code:
gnome-screenshot -a -c
For other useful gnome-screenshot command, from the terminal: gnome-screenshot --help
For Gnome, copying portion of the screen to clipboard is Ctrl+Shift+PrtScrn.