Key remapping with modifier keys

Question

I have a US keyboard by I'm using a British keyboard layout.

The US keyboard doesn't physically have the keys \ (backslash) and | (vertical bar).

I'd like to remap them to Alt # and Alt ~ respectively.

How can I achieve this?

I'm running Ubuntu Artful, which uses xkb.

Answer 1

It's not crystal clear what you mean, but possibly you want to edit the /usr/share/X11/xkb/symbols/gb file and change the line

key <BKSL>  { [numbersign, asciitilde,   dead_grave,   dead_breve ] };

to

key <BKSL>  { [numbersign, asciitilde,    backslash,          bar ] };

Result:

Right Alt + # => \

Right Alt + Shift + # => |