Implementing a simple shell in C designed to run on a linux based system

Commands: • calc expr. - prints out the result of the mathematical prefix expression that comes after the command. • time - prints out the current local time and date • path - prints out the current working directory • sys - prints the name and version of the OS and CPU type • put dirname filename(s) [-f] – put files filenames in the directory dirname • get filename - prints the content of the file filename to the screen • quit - ends the program

Notes: • If the command is not one of the above, you should print an error message and wait for a new command. • You can assume the expression after the calc command is a valid prefix expression containing only ‘+’ and ‘–‘ signs. You can also assume a space character separates any two numbers/signs. e.g. “+ + 2 3 - 4 5”. • Note that if you want to use the prefixadd() function from week 2 workshop you will need to store the expression as a ragged array of strings. • time – you can use the functions defined in <time.h> (link). Hint: look at time(), localtime() and asctime() functions. • path - you can use the linux system function getcwd() (link). • put - The put command will create a new directory called dirname and copy the file (or files) listed in the command, in this directory. If the directory exists you should only print an error message, unless -f has been specified, in which case the directory will be completely overwritten (old content is deleted). If a file(s) doesn’t exist, you will need to print a ‘file not found’ message for that file. • get - The get command will dump the file contents to the screen 40 lines at a time and pause, waiting for a key to be pressed before displaying the next 40 lines etc.