First of all, I assume that you are using awesome 3.4.something since you tagged this as ubuntu. Then: You don't specify key for your shortcut, only modifiers. And lastly: you should use full path for command you want to run and put it in double quotations.
See example for binding Shift-e to run script from user home folder:
awful.key({ modkey, "Shift" }, "e", function () awful.util.spawn("sh /home/USERNAME/myscript.sh") end),