This document provides an overview of the Linux operating system and commands. It begins with course objectives to introduce Unix concepts, commands, and the VI editor. It then discusses what an operating system is and why they are needed before exploring the evolution, flavors, and architecture of Unix/Linux. Key topics covered include the file system structure, absolute vs relative paths, how Unix sessions work, login sequences, command syntax, and standard input/output/error. The document also examines regular expressions, shell metacharacters, editors like VI, and permissions.

1. Linux Commands Summary

2. Course Objective
 To introduce the Unix Operating System Concept.
 To introduce standard Unix commands.
 To introduce VI editor.

3. References
 Text Book Reference
 Brain W. Kernighan and Rob Pike, The UNIX Programming
Environment.
 A Practical Guide to Linux® Commands, Editors, and Shell
Programming - Mark Sobell's
 Web Reference
 Unix Tutorial For Beginners
 Introduction to Unix
 http://www.cis.uab.edu/cs344/spring2005/

4. What is Unix Operating System
 Unix OS is a Program
 Unix OS provides interface
between users and bare
hardware
 Unix OS manages
resources: CPU(s),
memory, disks, other I/O
devices.
Operating System
users

5. Why do we need Operating System ?
To Interact with Computer Hardware
End User
Computer Hardware
Operating-System
Utilities
Application
Programs
OS Designer
System Programmer
Application Programmer
E.g.
compiler, librari
es, shell
E.g.
database, web
servers

6. Evolution of Unix OS

7. Flavors of Unix
 AIX (Advanced IBM Unix)
 HP-UX ( Hewlett Packard Unix)
 BSD ( Berkeley Software Distribution. )
 SCO UNIX
 SOLARIS
 LINUX, etc

8. System Architecture
HARDWARE
KERNELDATABASE
UNIX
COMMANDS
COMPILERS
OTHER
APPLICATIONS
PACKAGES
SHELL
SHELL
SHELL
SHELL
User
UserUser
User

9. System Architecture
 Major components of Unix are :
 Kernel
 Monitors and controls hardware resources
 Allocates them among its users in an optimal manner
 Utilities
 Programming tools that do standard tasks extremely well.
 EX: cp, grep, awk, sed, bc, wc, more
 Shell
 Command Line Interpreter.
 Provides a processing environment for the user programs.
 User Applications
 Programs written by the user

10. Processing Environment
• User Program
– Set of instructions written by the user
• Process
– Instance of a program under execution
• Shell
– Provides a processing environment for the user programs

11. Structure of Unix File System

12. Absolute Path and Relative Path
 The Absolute Path
 The entire pathname starting from root(/)
 Example
 /home/oresoft/.
 The Relative Path
 The path relative to your present working directory
 Example
 cd ..

13. How Unix Session Works.
USER TYPES COMMAND
SHELL EXECUTES
UTILITY TO CARRY
OUT COMMAND
SHELLASKS FOR A COMMAND
USER INTERACTS WITH
UTILITY
SHELL PROMPTS FOR
NEXT COMMAND
USER TYPES CONTROL-D
LOGOUT
LOGIN

14. Login Sequence.
 /etc/passwd 1
 /etc/shadow 2
 /etc/group 3
 /etc/profile 4
 /etc/profile.d/*.sh 5
 ~/.bash_profile 6
 ~/.bashrc 7
 /etc/bashrc 8

15. Unix Command Structure
 Unix Command line structure
 command [options] [arguments]
Refer the following word Doc for Detail Command

16. Concept of stdin, stdout and stderr
Operating System
Another
Computer
program running
stdout
stderr
stdin
Keyboard
A Computer
program running
stdout
stderr
stdin
Monitor

17. Standard Files
 Standard Input (0)
 This file is opened by shell to accept information.
 Standard Output (1)
 This file is opened by shell to direct output
 Standard Error (2)
 This file is opened by shell for writing error messages

18. Regular Expressions
What is it?
 String of ordinary and metacharacter which can be used to
match more than one type of pattern.
 Uses character set
 * , [], ^, $, {}, etc.

19. The Shell Metacharacters.
 See Demo at
/home/oresoft/Training/Linux/commands/shellChar
 * - Matches all filenames in current directory.
 ? - Matches a single character.
 [abc] - Matches a single character – either a, b or c.
 [!abc] - Matches a single character – which is not a, b or c.
 [a-c] – Matches a single character which is within the range of a and c.
 ^abc – Matches the pattern abc at the beginning of the line.
 abc$ - Matches the pattern abc at the end of the line.

20. Editor in Unix
 Need for editor in Unix
 Types of editor
 Line Editor
 ed : UC Berkeley
 ex : Powerful than ed, Bell Systems
 Full Screen Editor
 vi (stands for visual)
 vim – vi improved
 emacs (GNU)

21. The vi Editor.
 The important characteristic features are:
 Omnipresent
 Works on different Unix flavors
 Fast
 Various operations are very fast
 Powerful UNDO features
 Text in lines could be undone with very less effort

22. The vi Editor.
 The limitations are:
 Less user-friendly
 No graphical user interface
 Highly Case-sensitive
 Letter in small case has a different implementation in comparison
with the same letter in upper case
 Keystrokes could have more than one meaning
 A letter (of the same case) has different implementation across
different modes.

23. The vi Editor.
 Modes of working:
 Command Mode
 Keys are interpreted as commands
 Insert Mode
 Keys are interpreted as data
 Escape Mode
 Keys are interpreted for saving/exiting purposes

24. vi Operating modes.
Command mode
Insert mode
i, I , o, O, a, A ..
esc
Last line mode
Enter:
:q

25. Vi editor commands
 To move around
 h, j, k, l, ^D, ^U, G, 0, ^, $, w, b
 Inserting/Deleting text
 i, a, I, A, r, R, o, O, dd, dw, c$, D, x, X.
 Changing/Replacing text.
 cc, cw, c$, ~, J, u, . , yy, yw, p, P
 File manipulation.
 :w, :wq, ZZ, :w!, :q, :q! , :![command]

26. Searching a pattern
 /pattern
 Searches forward for first occurrence of a pattern.
 ?pattern
 Searches backward for first occurrence of a pattern.
 n
 Repeats the last search.
 N
 Repeats the last search command in opposite direction.

27. Pattern Substitution.
 :s/ptn1/ptn2
 Replaces first occurrence of ptn1 with ptn2.
 : s/ptn1/ptn2/g
 Replaces all occurrences in the current line.
 : m, n s/ptn1/ptn2/g
 Replaces all occurrences in lines m to n.
 : ., $ s/ptn1/ptn2/g
 Replaces all occurrences from current line to end of file.

28. Customizing vi.
 The set command
 :set all
 :set nu
 The abbr command
 :abbr itl ―Infosys Technologies Ltd‖
 The map command
 :map ^X :wq

29. System Variables.
 PATH
 Search path referred by Unix for any command.
 echo $PATH
 HOME
 Indicates the home directory for the user.
 echo $HOME

30.  set command
 Used for display all the environment variables.
 Shows the current values of system variables.
 Also allows conversion of arguments into positional parameters.
 Syntax : set
set command.

31. File Permission - Absolute Mode.
r w x r w x r w x
4 2 1 4 2 1 4 2 1
Owner Group Other
Group OthersOwner
rwxrwxrwx
Permission Value
R 4
W 2
x 1
- No Permission

32. Summary
 Background
 Features of Unix
 Unix System Architecture
 Unix File System
 General Unix commands and utilities
 Processes
 Regular Expressions
 Vi Editor
 Modes of operation

33. File Permission – Symbolic Mode.
Who User Class Meaning
U User Owner of file
G Group Group to which owner
belongs
O Other All other Users
Who Meaning
r Sets read permission
w Sets write permission
x Sets exec permission
Symbolic mode user class specification
Symbolic mode permissions

34. Examples of chmod
 Syntax.
chmod [0-7][0-7][0-7] filename (Absolute
Mode)
chmod [ugo][+-][rwx] filename (Symbolic
Mode)
$ chmod a=rw temp
$ ls -l temp-rw-rw-rw- 1 alex pubs 57 Jul 12 16:47 temp

35. Unmasking File Permission
 umask
 Stands for user creation mask.
 Sets default permissions for a newly created file and directory.
 The value can be changed.
Example
6 6 6 - System wide default permissions
- 0 2 2 - Denial ‗mask‘ set by UMASK
6 4 4 - Resultant permissions that will be
set on all files created (-rw-r—r--)