Shell programming

GNU has done an impressive job of unifying the *nix with a set of common tools, and the fact that someone can "brew install coreutils" and get a bunch of useful binaries is a testament to the value of the work GNU has done. BUT...

That does not mean that "shell" is the best language, it just means that shell is the least common denominator for interacting with a diverse set of programs (and it has served *nix well). Text input/output, flags for program options, silence is success, integer return codes, etc... As programs mature they get split into libraries, and those libraries get external interfaces to other languages like python/ruby/etc...