Part XIII: The Shell and Programs

What are we making?

This is the final part of the guide. You deserve a pat on the back for coming this far. This chapter will end in us making a program called a shell. Different kinds of shells for different operating systems can do many different things, but, a shell is a user space program that lets you interact with the computer by typing commands.

Our shell will have the following functionality:

• ls [directory] to list the entries in a directory.
• mkdir [path] to make a new directory in the file system.
• touch [path] to make a file in a directory.
• rm [path] to delete files and directories.
• run [path] to run programs stored within the file system.
• cat [path] to read from files.
• write [path] to read to files.

This is all I will be instructing you on how to implement, but this is another part where you can become creative and make your own commands.

There may be confusion in the run command. "How can we get files to run when there is no way to store them in the file system?" This is where MKFS comes in.

MKFS means "make file system" and is a piece of software we will be writing for the host operating system. It will copy all the files and directories in a special directory on the host operating system (called rootfs) to the file system that our custom operating system will be using. The compiled binaries for user space programs are then stored somewhere within rootfs which are then be ready to be loaded into memory from the file system in the custom OS.

Let's get into writing the MKFS.