Write a simple single thread CSC4420 shell, i.e., no concurrent commands, to support at least the following built-in commands: o prompt can set to any string you input, in addition to the current history event number, i.e, %h as in csh; o url : list the course web site o hour : list class times o room : list classroom location o desp: list the description of this course o text: list the textbook o ref: list the reference books o prof: list the professor's name o pol : professor's office location o poh : professor's office hours opma : professor's email address o ta : list the TA's name otol : TA's office location o toh : TA's office hours otma : TA's email address o history : list history of events up to the number you set o help : list all the available commands o exit or quit : exit CSC4420 shell