I'm strongly considering making it a point to do just that: include Ruby in all the images I can, just to not have to use Bash. For one-liners it's fine, but I don't get ten lines into a Bash script before missing scripting-language features. However, if someone were to try to talk me out of what they consider to be an absurd notion, I would be prepared to take their criticism seriously.
I have multiple ~10 line POSIX shell scripts in my dotfiles. I also have a bunch each of Perl and Python ones [1]. I'd rather not rewrite my shell scripts with neither of that languages, or Ruby (which I like and use a bit).
When scripting, I find general-purpose languages are better when you have structured data (i.e. some JSON coming in) or you want to use libraries, and shell scripting better when you're wiring up multiple programs to work together, or starting up a program after setting up the environment for it.
IIRC, the FreeBSD sh(1) man page was a good entry to writing POSIX compliant, thus quite portable shell scripts.
