Dependencies are another huge issue if you want to be cross-platform. A Ruby script (for example) relies on the Ruby interpreter, which works the same cross-platform. If it has other dependencies, there's an established way to declare and install them.
In contrast, a bash program calls out to lots of little programs: sed, awk, grep, etc. Different platforms have different implementations which take different flags, etc.
My friend and I just spent a couple of days getting some bash scripts that ran fine under Cygwin to also run on OSX. It was painful.
Ruby system scripts assuredly do not work the same cross-platform, particularly if they have to call to C libraries. Expect to have to rejigger them just as you would bash.
Use a modern scripting language like Python or Ruby otherwise you are entering a world of pain.
http://mywiki.wooledge.org/BashPitfalls