A Quick Look at the Unix Operating System

What is an Operating System?
An operating system is a program that provides an interface between:

... 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).

Standard I/O
Full Name Abbrev Meaning Comment
Standard Input stdin A user typing at the keyboard  
Standard Output stdout Outputting to the terminal screen Buffered: Regardless of when output statements occur in the program, outputting doesn't happen until a bunch of text has been saved up.
Standard Error stderr Outputting to the terminal screen Unbuffered: Outputting happens as soon as an output statement is executed.

Redirecting I/O
Instead of input coming from a live user at the keyboard, or output going to the terminal screen, 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, 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 neem1883 has a home directory
in which there's a subdirectory CS1313, and in the CS1313 subdirectory is a file named my_number.c, then the path of my_number.c 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 or directory 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.

This webpage: http://cs1313.ou.edu/unix.html