Shelly is a simple implementation of a shell in C, that is it is only able to interpret single line commands. It demonstrates the basics of how a shell works. That is: read, parse and exec. Reading and parsing is done via a lexical analyzer and LALR parser both generated using linux built-in utility lex and yacc, respectively. Since its purpose is demonstration (not feature completeness or even fitness for casual use), it has many limitations, including:

Commands must be on a single line. Arguments must be separated by whitespace. No quoting arguments or escaping whitespace. No piping or redirection.

This code is in the public domain (see UNLICENSE for more details). This means you can use, modify, and distribute it without any restriction. I appreciate, but don't require, acknowledgement in derivative works.