Please help with 1 macro

Hello gamers?How’s life?
So,as the title says …I want to make a macro that dose this:
Cast Power word shield on my focus target if i have one
Cast penance at my focus target’s target if i have one
Cast penance on my target if I don’t have a focus target
Now…I know i need to use “nodead” “Help” “Exist” but I never actually understood how these work
TLDR : with tank @ my focus target,Shift press it ,cast power word shield on tank,nomod cast penance on my tank’s target,if i don’t have tank @ focus,to cast penance @ my target
So,I’m trying something like this :
#showtooltip
/cast [mod:shift @focus] power word: shield ; [nomod @focus,nodead,help] penance , penance
but ofc ain’t working…the shift power word @ focus part works,but the penance part dose not
Can anyone please help a noob?
have a nice day mates!

#showtooltip
/cast [mod:shift,@focus] Power Word: Shield; [@focustarget,harm,nodead] [] Penance

thank mate!you are my Hero! it works