Implemented:

*   all built-in commands fully implemented and working
*   able to recognize non-built-in commands and their argument, and successfully execute command
*   File I/O
*   piping
*   wildcard matching
*   environment variable expansion
*   tilde expansion
*   background processes
*   standard error redirection


Not Implemented:

*   piping with aliases
*   bug: environment variables in quotes add unnecessary spaces to string
*   filename completion with escape key
*   can't read commands from input file