unix: avoid using non-portable `read -p' `read -p' is not POSIX-compatible, but bash-compatible. See [0], [1]. Thus replace it with `printf' and `read' combo that does the same, but still conforms with POSIX. [0]: http://pubs.opengroup.org/onlinepubs/9699919799/utilities/read.html [1]: https://www.gnu.org/software/bash/manual/bashref.html#index-read