Write a simple single thread shell , i.e., no concurrent commands, to support at least the following built-in commands: You can use arbitrary placeholders for the info.

prompt can set to any string you input, in addition to the current history event number, i.e, %h as in csh;

url : list the course web site

hour : list class times

room : list classroom location

desp : list the description of this course

text : list the textbook

ref : list the reference books

prof : list the professor's name

pol : professor's office location

poh : professor's office hours

pma : professor's email address

ta : list the TA's name

tol : TA's office location

toh : TA's office hours

tma : TA's email address

history : list history of events up to the number you set

help : list all the available commands

exit or quit : exit shell