Introduction to Unix

CS240 Computer Science II

The UNIX Environment

Hardware

UnixKernel

Shell

Typical UNIX File System

Important Directories and Files

• / (root): the top of the file hierarchy• /export/home: usually contains all users’ subdirectories.• /usr: traditionally contains subdirectories that keep

system information.• /usr/bin: usually contains the standard Unix utilities.• /usr/sbin: contains utilities for system administration.• /etc: keeps configuration and other administration files,

e.g., /etc/passwd contains a list of all users.• /var: contains files that vary as the system runs, e.g.,

users’ mailbox files, system log files, etc.• /dev: contains information about peripheral devices.• /tmp: used by programs to hold temporary files.

Unix Standards

• Two groups– System V: led by AT&T and Sun Microsystems;

newest version is System V Release 4.– BSD (Berkeley Standard Distribution): the Open

Software Foundation (OSF) led by IBM and HP; newest version is OSF/1.

• Both standards conform to standards set by Portable Operating System Interface (POSIX).– Solaris from Sun Microsystems– AIX from IBM– HP-UX from Hewlett Packard– IRIX from Silicon Graphics

Commercial Unix Systems

UNIX

System V BSD

V.2

V.3

V.4

V.4.1

4.2

4.3Apollo

HP/UXSun OS

IBMAIX

OSF/1

Utilities or Utility Programs

• More than 200 application programs such as editors, graphic user interface, search and sort routines, and some shell programs are integrated into the standard Unix operating system. Many other commercial and free programs such as compilers, spreadsheets, and desktop publishing tools are available and can be easily added to the system.

The Shell

• A shell is a command interpreter; it interprets the command enter by a user and calls the program the user wants.

• A shell can be used as a high-level programming language in that shell commands can be arranged and stored in a file for later execution.

• There are three popular shells in use today: the Bourne, the C Shell, and the Korn Shell. Korn shell is a superset of Bourne shell. A user may specify the shell he or she wants to use.

Run a Utility Program in a Shell

• Each utility program is uniquely identified by its name such as passwd, date, or ls, etc. To run a utility, just type in the name of the utility and press the enter key.

Frequently Used “Directory” Related Utilities

• pwd: displays current directory.• mkdir: creates a new subdirectory.• cd: changes to another directory.• rm: removes a file.• rmdir: removes a directory.• ls: lists contents of the current directory.• which: displays the full path name of a utility.• whereis: displays the pathname of a utility.

Frequently Used “File” Related Utilities

• pico: starts the “pico” text editor• vi: starts the “visual” text editor.• cat: displays the content of a file.• wc: counts the words in a file.• cp: copies a file.• more, page, head, tail: displays the content of a file.• file: displays information about the contents of a file.• diff: displays the difference between two files.• grep: searches for a particular strings in a file.• sort: orders a file by lines.• mv: renames a file.• lp: prints a file.• lpstat: displays the status of all print jobs.• cancel: removes specified jobs from the printer queue.• chmod: specifies the accessibility of a file.• ln: makes a link to an existing file.

Other frequently used utilities• passwd: changes password.• date: displays today’s date.• clear: clears the screen.• man: displays information about a particular utility.• groups: displays list of all the groups to which the user belongs.• mail, mailx: sends and reads emails.• who: • finger: displays information about users.• write: sends a message to another user who is logged in.• talk: initiates a online conversation with another user who is logged

in.• compress: compresses a file.• uncompress: restores a compressed file.

List of commands with more detailed discussions

• man• ls• vi• pwd• mkdir• rmdir• more• mailx• chmod

The man command

• lklm,

The ls command

The three modes of vi Editor

C o m m a n dM o d e

InputM ode

Last-lineM ode

Escape

Insert,Append,

Open,replace,Change

Return

:

Fucntions of the three mode in vi

• Input mode: allows text such as source code to be entered.

• Command mode: allows various commands to be entered for text editing and other purposes. Several commands such as insert, append, open, replace, and change that are issued in the command mode will take you to the input mode.

• Last-line mode: all commands that start with a colon : puts vi in the last-line mode.

Note: all text entered is temporarily kept in a buffer until permanently saved to disk.

Starting vi

Command Function

vi filename Create/edit filename starting a line 1.

vi +n filename Edit filename starting a line n.

vi + filename Edit filename starting last line.

vi -r filename Recover filename after a system crash.

Adding text filename: from command to input mode; must press Escape key to return to

command mode

Command Insert text

i Before the cursor.

I Before first non-blank character on line.

a After the cursor.

A At the end of the line.

o Open a line below the current line.

O Open a line above the current line.

Some moving cursors in the command mode

Command Cursor movement

Space, I, or Space to the right

H or Space to the left

w or W Word to the right or blank-delimited word to the right.

b or B Word to the left or blank-delimited word to the left.

$ End of the line.

0 Beginning of the line.

Miscellaneous Commands

Command Effect

:w filename Store contents of buffer to filename.

:q Quite vi.

:q! Quite vi with saving contents of buffer.

~ Change upper case to lower case and vice versa.

ZZ Store content of buffer and quit vi.

:f or Ctrl+G Displays the filename, the status,the current line number, the number of lines in the buffer, etc.

viewing different parts of the buffer in the command mode

Command Cursor movementCtrl + D Down (forward) one-half screen.

Ctrl + U Up (backward) one-half screen.

Ctrl + F Down (forward) one full screen.

Ctrl + B Up (backward) one-full screen.

nG To line n or to the last line if without n.

H To the top of the screen.

M To the middle of the screen.

L To the bottom of the scren.

Customizing the vi environment: the set command

• In the command mode type :set followed by a parameter listed below and press enter key.– all: lists a complete list of parameters and their current status.– atuoindent (or ai) creates tab stops; Ctrl+T tabs right and

Ctrl_D tabs left. noautoindent or noai turns off autoindent feature.

– shiftwidth=nn sets the spacing (#characters) between tab stops – number to display line numbers; nonumber remove line

numbers.– wrapmargin=nn, where nn is arbitray positive integer

representing # characters after which wrap-around takes place.– showmode displays the mode type; noshowmode removes the

display.• Note that the parameters can be permanently set in a

user’s startup file .profile With Bourne or Korn shell, or .login with C shell. The parameters may also be set in a .exrc file.