Because they're used to using Ruby. The efficiency difference is negligible. $ time sh -c exit real 0m0.002s user 0m0.001s sys 0m0.000s $ time ruby -e exit

Because they're used to using Ruby. The efficiency difference is negligible. $ time sh -c exit real 0m0.002s user 0m0.001s sys 0m0.000s $ time ruby -e exit real 0m0.009s user 0m0.008s sys 0m0.000s OTOH I do agree that it is a bit silly to start a Ruby interpreter if you're only going to use it to shell out :)