ported to POSIX sh

[joh6nn]

I needed repl on boxes that I'm not able to install Ruby on (for a variety of reasons). So, for greater portability, I ended up porting it to (what I hope is) POSIX compliant sh. In my tests, it was 99% compatible with your original; the only two differences are exiting on ^C instead of on ^D, and the addition of a --version flag.

I don't expect you to do much (anything?) with this, but I didn't know what else to do with it except contribute it back.

https://github.com/joh6nn/repl/tree/POSIX-sh