When I execute a command using `ProcessBuilder`, how does it know where to look for that command? Using [this hack/trick](https://stackoverflow.com/questions/318239/how-do-i-set-environment-variables-from-java) I've modified my PATH variable (verified by inspecting `processBuilder.environment()`) to be bad (empty, working dir, etc) but ProcessBuilder can still execute sort, echo, bash, etc. just fine. How is it doing this?!

Note: My particular development environment is OSX but this code will also run on Red Hat Enterprise Linux.