Problem: write a simple shell myshell that has the following properties: Design a simple command line shell that satisfies the below criteria and implement it on a Linux platform. The shell must support the following internal commands:

- cd - change the current default directory to . If the directory argument is not present, report the current directory. If the directory does not exist an appropriate error should be reported. This command should also change the PWD environment variable.

- clr clear the screen

- dir - list the contents of directory

- echo - display on the display followed by a new line (multiple spaces/tabs may be reduced to a single space)

- quit - quit the shell

Side notes:

All other command line input is interpreted as program invocation which should be done by the shell forking and executing the programs as its own child processes. The shell must support background execution of programs. An ampersand (&) at the end of the command line indicates that the shell should return to the command line prompt immediately after launching that program. The command line prompt must contain the pathname of the current directory.