A Quick Look at the Unix Operating System

Hardware Examples

• I/O devices (e.g., keyboard, mouse, printer)
• CPU
• Main memory
• Secondary storage (e.g., hard disk, floppy disk, CDROM)

Examples of Operating Systems

• MS-DOS and Windows 95/98/NT/2000
• MacOS
• PalmOS
• Unix: comes in lots of flavors
  • AIX (made by IBM)
  • Solaris (made by Sun Microsystems)
  • Unicos (made by Cray)
  • IRIX (made by Silicon Graphics Inc)
  • HP-UX (made by Hewlett-Packard)
  • Linux (freeware that runs on PCs and other platforms)

What is Unix?

• Developed in the late 1960s/early 1970s at Bell Labs.
• Cryptic: most command names are 2 - 5 characters long.
• Text based like MS-DOS (because it's so old), not window based like Win98 or MacOS.
• Very efficient, powerful, reliable.
• Common in academic and research environments.
• Different flavors (e.g., Linux, AIX, IRIX) are not fully compatible but often are mostly compatible.
• Designed for people who already know everything about 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).

• man command
  Display the online documentation for a command. For example,
  man pwd displays the online documentation for the command pwd.
  man -k word gives a listing of all the commands related to word.
• date
  Today's date and time.
• pwd
  Print the name of the current (working) directory.
  In MS-DOS, by contrast, the current directory is included in the prompt:
  C:PROGS\MYPROGS>
• cd direc
  Change the current directory to a directory named direc.
  Like cd in MS-DOS.
• ls
  List the files and subdirectories in the current directory.
  Like dir in MS-DOS. You can get a more detailed listing of the current directory's contents: ls -l
  
• mv srcfile dstfile
  Move the file named srcfile to a file named dstfile (i.e., change its name).
  You can also use mv to move a file from one directory to another:
  mv srcfile dstdirec
  Like move in MS-DOS.
• cp srcfile dstfile
  Copy a file named srcfile to a new file named dstfile (or, if dstfile already exists, replace its contents with the contents of srcfile).
  Like copy in MS-DOS.
• rm thisfile
  Remove (delete) a file named thisfile.
  Like del in MS-DOS.
• mkdir newdirec
  Make a new directory called newdirec as a subdirectory of the current directory.
• rmdir olddirec
  Remove an empty subdirectory named olddirec.
• cat thisfile
  Output the contents of the file thisfile to the terminal.
  cat srcfile1 srcfile2 > dstfile
  Concatenate the contents of srcfile1 and srcfile2 (dump them out one after the other) and put the concatenated output into dstfile.
• more thisfile
  Output thisfile to the terminal in a controlled way.
• time command
  Determine how long it takes to run a command.
• mailx hneeman@ou.edu
  Send e-mail to hneeman@ou.edu.

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.

• program > outputfile
  The output of executing program goes into outputfile.
• program < inputfile
  The input needed for executing program come from inputfile.
• program < inputfile > outputfile
  The input needed for executing program come from inputfile, and the output goes into outputfile.
• program >> outputfile
  The output of executing program is appended to the end of outputfile.

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
/tmp_mnt/ecn/facstf1/neeman
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
/tmp_mnt/ecn/facstf1/neeman/CS1313
and the file's full name is
/tmp_mnt/ecn/facstf1/neeman/CS1313/mynumber.f90

Special Directories

• The root directory is denoted with a slash:
  /
• The home directory of a user named neeman is denoted
  ~neeman
• You can denote your own home directory as
  ~
• The current directory is denoted with a single period:
  .
• The parent directory of the current directory is denoted with two periods:
  ..