Answer the following questions to describe your code submission. Please keep
all lines to a maximum of 80 characters wide.

1 - Explain how you are keeping track of the return code for use in echo $?.

    After each process is executed in the shell's main loop, the "?" key is
    set to the return code of that process.

2 - Briefly describe how you are storing or deleting environment variales.

    Environment variables are stored directly in the hashmap. Export sets
    the value to the corresponding key in the hashmap. Unset removes the
    key from the hasmap. Echo finds the value in the hashmap based on the key.

3 - Consider the following three command lines:
      $ echo ${VAR}
      $ echo {VAR}
      $ echo ${VAR
    Briefly explain how your code processes each. Does your code handle bad
    input strings?

    In the first case, the correct environment variable is printed.
    In the second case the literal string {VAR} is printed.
    In the third case nothig is printed.
    In the first two cases the exit code of echo is 0 because they are both
    valid inputs to echo, but the third exits with a code 1 because the
    syntax is invalid.