Shift target player

Ok, I am having trouble creating a macro, my plan is to cast Power Word: Shield on myself when I hold shift but on my target otherwise. What I have so far does not work, anyone that could fix it?

#showtooltip
/cast [nomod] Power Word: Shield
/cast [mod:shift, @player] Power Word: Shield

You can try-
#showtooltip
/cast [@target,exists,nodead] Power Word: Shield; [@player] Power Word: Shield

I use this myself, except in the first bracket i use @mouseover,exists,nodead
and if you want to use it for focus, then mouseover or self-
#showtooltip
/cast [@focus,exists,nodead] Power Word: Shield; [@target,exists,nodead] Power Word: Shield; [@player] Power Word: Shield