My shell project that I created for the Systems Programming class at Purdue. Got over 100% on this project.

1. Features specified in the handout that work.
   Everything works including:
   Parsing and executing commands
   File redirection >, >>, <, >&, and >>&
   Pipes |
   isatty()
   Ctrl+C
   Zombie Elimination
   Exit the shell
   Quotes "" and ''
   Escaping special characters \
   Builtin Functions (printenv, setenv, unsetenv, source, cd)
   Source .shellrc file
   Source with environment variables
   Subshells $()
   Process substitution
   Environment variable expansion ${}
   Tilde expansion (~)
   Wildcarding (*, ?)
   Edit mode (arrow keys, Ctrl+D for delete, Ctrl+H for backspace, Ctrl+A for home, Ctrl+E for end)
   History up and down arrow keys
   Editing history commands
   Variable prompt

2. Features specified in the handout that do not work.
   Nothing

3. Extra features I have implemented.
   cd - . This returns to the last directory the user was in before the current directory. Also updates PWD and OLDPWD environment variables for all cd commands.
   $?, $_, $SHELL, $anything. Extra environment variable parsing without the curly brackets like zsh.
   Error statement if command not found