A Quick Look at the Unix Operating System

What is an Operating System?
An operating system is a program that provides an interface between hardware and users ... and so much more.

Hardware Examples

Examples of Operating Systems

What is Unix?

Files & Directories
Unix files and directories are very much like files and directories (folders) in Windows and MacOS.

Basic Commands
All commands must be typed exactly right, or they will fail (or do something other than what you want).
Unix is case sensitive; it matters very much whether a letter is upper case (capital) or lower case (small).

Redirecting I/O
Instead of input coming from the keyboard or output going to the terminal, they can be redirected from or to a file.

Root Directory
The root directory (which is denoted by a slash /) is the topmost directory; all other directories are subdirectories of it.
It's like the "My Computer" icon in Windows 98/NT, or like the desktop in MacOS.

Directory Paths
The full name of a directory, starting from the root, is called a path. The full name of a file is its path, a slash and its filename. So, if a user neeman has a home directory
in which there's a subdirectory CS1313, and in the CS1313 subdirectory is a file named mynumber.f90, then the path of mynumber.f90 is
and the file's full name is

Special Directories

Asterisks indicate parts of a filename that could be anything.

File Permissions
The person who owns a file gets to decide who can read it, who can write to it, and, if it's an executable, who can execute (run) it.

Paul DuBois, Using csh & tcsh. O'Reilly & Associates, 1995.
Daniel Gilly, Unix in a Nutshell, System V edition. O'Reilly & Associates, 1992.
Rebecca Thomas & Jean Yates, A User Guide to the Unix System. Osborne/McGraw-Hill, 1982.