Code:
on join:
if player has permission "join.silent":
set join message to ""
else if player does not have permission "join.silent":
set join message to "&b%player% &ajoined"
loop all players:
if loop-player has permission "join.alert":
message "&7&o[%player%&7&o: &7&osilently joined&7&o]" to loop-player