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This presentation summarizes Useful Linux Commands.
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Linux Commands Summary
Course Objective
To introduce the Unix Operating System Concept.
To introduce standard Unix commands.
To introduce VI editor.
References
Text Book Reference Brain W. Kernighan and Rob Pike, The UNIX
Programming Environment. A Practical Guide to Linux® Commands, Editors, an
d Shell Programming - Mark Sobell's
Web Reference Unix Tutorial For Beginners Introduction to Unix http://www.cis.uab.edu/cs344/spring2005/
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
Why do we need Operating System ?
To Interact with Computer Hardware
End User
Computer Hardware
Operating-System
Utilities
ApplicationPrograms
OS Designer
System Programmer
Application Programmer
E.g. compiler, libraries, shell
E.g. database, web servers
Evolution of Unix OS
Flavors of Unix
AIX (Advanced IBM Unix) HP-UX ( Hewlett Packard Unix) BSD ( Berkeley Software Distribution. ) SCO UNIX SOLARIS LINUX, etc
System Architecture
HARDWARE
KERNELDATABASE
UNIX
COMMANDS
COMPILERS
OTHER
APPLICATIONS
PACKAGES
SHELLSHELL
SHELLSHELL
UserUser
UserUserUserUser
UserUser
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
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
Structure of Unix File System
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 ..
How Unix Session Works.
USER TYPES COMMAND
SHELL EXECUTESUTILITY TO CARRYOUT COMMAND
SHELL ASKS FOR A COMMAND
USER INTERACTS WITH UTILITY
SHELL PROMPTS FOR NEXT COMMAND
USER TYPES CONTROL-D
LOGOUT
LOGIN
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
Unix Command Structure
Unix Command line structure command [options] [arguments]
Refer the following word Doc for Detail Command
Concept of stdin, stdout and stderr
Operating System
AnotherComputer
program running
stdout
stderr
stdinKeyboard
A Computerprogram running
stdout
stderr
stdin
Monitor
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
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
* , [], ^, $, {}, etc.
The Shell Metacharacters.
See Demo at
/home/oresoft/Training/Linux/commands/shellChar
* - Matches all filenames in current directory.
? - Matches a single character.
[abc] - Matches a single character – either a, b or c.
[!abc] - Matches a single character – which is not a, b or c.
[a-c] – Matches a single character which is within the range of
a and c.
^abc – Matches the pattern abc at the beginning of the line.
abc$ - Matches the pattern abc at the end of the line.
Editor in Unix
Need for editor in UnixTypes 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)
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
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.
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
vi Operating modes.
Command mode
Insert mode
i, I , o, O, a, A ..
esc
Last line mode
Enter :
:q
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]
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.
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.
Customizing vi.
The set command :set all :set nu
The abbr command :abbr itl “Infosys Technologies Ltd”
The map command :map ^X :wq
System Variables.
PATH Search path referred by Unix for any command. echo $PATH
HOME Indicates the home directory for the user. echo $HOME
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.
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
rwxrwxrwxPermission Value
R 4
W 2
x 1
- No Permission
Summary
BackgroundFeatures of UnixUnix System ArchitectureUnix File SystemGeneral Unix commands and utilitiesProcessesRegular ExpressionsVi EditorModes of operation
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
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
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--)