Create a command$-$line shell program like bash or Powershell. Have a prompt, example below.

Reads from input, writes to output. until "quit" or "exit".

Implement $"$cd$"$ and $"$pwd$".($directly$).$ cd must take a full or relative path.

Implement the setting, deleting $($unsetting$)$ and getting of xsh environment vars:

xsh# set FOO banana

xsh# echo My favorite fruit is a $FOO.

My favorite fruit is a banana.

xsh# unset FOO

xsh# echo I$\text{'}$d love to eat a $FOO colored slug.

I$\text{'}$d love to eat a$$ colored slug.