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Linux Command Suumary

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This presentation summarizes Useful Linux Commands.
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  • 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 ProgrammingEnvironment. A Practical Guide to Linux Commands, Editors, and ShellProgramming - Mark Sobells 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 interfacebetween users and barehardware Unix OS managesresources: CPU(s),memory, disks, other I/Odevices.Operating Systemusers
  • 5. Why do we need Operating System ?To Interact with Computer HardwareEnd UserComputer HardwareOperating-SystemUtilitiesApplicationProgramsOS DesignerSystem ProgrammerApplication ProgrammerE.g.compiler, libraries, shellE.g.database, webservers
  • 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 ArchitectureHARDWAREKERNELDATABASEUNIXCOMMANDSCOMPILERSOTHERAPPLICATIONSPACKAGESSHELLSHELLSHELLSHELLUserUserUserUser
  • 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 COMMANDSHELL EXECUTESUTILITY TO CARRYOUT COMMANDSHELLASKS FOR A COMMANDUSER INTERACTS WITHUTILITYSHELL PROMPTS FORNEXT COMMANDUSER TYPES CONTROL-DLOGOUTLOGIN
  • 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 stderrOperating SystemAnotherComputerprogram runningstdoutstderrstdinKeyboardA Computerprogram runningstdoutstderrstdinMonitor
  • 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 ExpressionsWhat is it? String of ordinary and metacharacter which can be used tomatch 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 comparisonwith the same letter in upper case Keystrokes could have more than one meaning A letter (of the same case) has different implementation acrossdifferent 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 modeInsert modei, I , o, O, a, A ..escLast line modeEnter::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 $HOME
  • 30. set command Used for display all the environment variables. Shows the current values of system variables. Also allows conversion of arguments into positional parameters. Syntax : setset command.
  • 31. File Permission - Absolute Mode.r w x r w x r w x4 2 1 4 2 1 4 2 1Owner Group OtherGroup OthersOwnerrwxrwxrwxPermission ValueR 4W 2x 1- No Permission
  • 32. Summary Background Features of Unix Unix System Architecture Unix File System General Unix commands and utilities Processes Regular Expressions Vi Editor Modes of operation
  • 33. File Permission Symbolic Mode.Who User Class MeaningU User Owner of fileG Group Group to which ownerbelongsO Other All other UsersWho Meaningr Sets read permissionw Sets write permissionx Sets exec permissionSymbolic mode user class specificationSymbolic mode permissions
  • 34. Examples of chmod Syntax.chmod [0-7][0-7][0-7] filename (AbsoluteMode)chmod [ugo][+-][rwx] filename (SymbolicMode)$ 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.Example6 6 6 - System wide default permissions- 0 2 2 - Denial mask set by UMASK6 4 4 - Resultant permissions that will beset on all files created (-rw-rr--)
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