为什么以及何时使用shell而不是Ruby

Since I am conversant in Ruby, I am about to script a few things on OSX using it. But then I thought, perhaps I am missing the boat. I know a lot of reasons to prefer Ruby over Bash (or whatever sh-compatible command language interpreter), but I don't know any reasons not to. What is the upside of programming the shell directly?Since I am conversant in Ruby, I am about to sc