Firstly, open your terminal and type 'echo $PATH', to see a list of directories within your computer. Copy this output and paste it in the shell_init file in order to specify the PATH environment variable. In order to to run this shell, in your terminal, navigate to the directory containing these files, and then type 'make' in order to create the executable file needed to run the shell. Then, type './shell -i shell_init' into your terminal in order to start the shell.