This is a bash script for Ubuntu which registers a keyboard shortcut.

register-shortcut.sh

#!/bin/bash

if [ "$#" -ne 3 ]; then
	echo "Usage: $0 name command binding"
	echo "Example: $0 \"screenshot\" \"gnome-screenshot\" \"<Primary><Alt>s\""
	exit
fi

GSETTINGS_PATH="org.gnome.settings-daemon.plugins.media-keys"
KEY_PATH="/org/gnome/settings-daemon/plugins/media-keys/custom-keybindings"
GSETTINGS="gsettings set $GSETTINGS_PATH.custom-keybinding:$KEY_PATH"

i=0
while [ "$(gsettings get $GSETTINGS_PATH.custom-keybinding:$KEY_PATH/custom$i/ name)" != "''" ]
do
	i=$(( $i + 1 ))
done

CK=$(gsettings get $GSETTINGS_PATH custom-keybindings)
if [ "$CK" == "@as []" ]; then
	gsettings set $GSETTINGS_PATH custom-keybindings "['$KEY_PATH/custom0/']"
else
	gsettings set $GSETTINGS_PATH custom-keybindings "${CK%]}, '$KEY_PATH/custom$i/']"
fi

$GSETTINGS/custom$i/ name "$1"
$GSETTINGS/custom$i/ command "$2"
$GSETTINGS/custom$i/ binding "$3"