Shell Expansion
expand is a python program that uses regular expressions to implement some of the functionalities of Parameter Expansion as in the GNU Bash Unix Shell (can read about this at https://www.gnu.org/software/bash/manual/html_node/Shell-Parameter-Expansion.html).
By using a single regular expression, most of the parameter expansion functionality provided in the GNU Bash Unix Shell is replicated in this python program.
To run the program type "python expand.py" and then type in whatever you want like you in GBU Bash. As described in the link provided in the firs paragraph of this file, the '$' character introduced parameter expansion.
Also provided is a visual representation of the regular expression that provides the crux of this program's functionality.