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 STEP 1: THERE ARE THREE CLASSES OF FILE PERMISSSIONS FOR THE THREE CLASSES OF USERS:THE OWNER (OR USER) OF THE FILE.THE GROUP THE FILE BELONGS TO,AND ALL OTHER USERS OF THE SYSTEM. $IS -1 -RWXR-XR-- THE FIRST THREE OF THE PERMISSION FIELD REFER TO THE OWNER'S PERMISSIONS;THE SECOND THREE TO THE MEMBERS OF THE FILE'S GROUP;AND THE LAST TO ANY OTHER USERS.THE FIRST THREE LETTERS,RWX,SHOW THAT THE OWNER OF THE FILE CAN READ IT,WRITE (W) IT,AND EXECUTE (X) IT. THE SECOND GROUP OF THREE CHARACTERS,R-X,INDICATES THAT MEMBERS OF THE GROUP CAN READ AND EXECUTE THE FILE BUT CANNOT WRITE IT,THE LAST THREE CHARACTERS,R-X,SHOW THAT ALL OTHERS CAN READ AND EXECUTE THE FILE BUT NOT WRITE TO IT. IF YOU HAVE READ PERMISSION FOR A FILE ,YOU CAN VIEW ITS CONTENTS.WRITE PERMISSION MEANS THAT YOU CAN ALTER ITS CONTENTS.EXECUTE PERMISSIONS MEANS THAT YOU CAN RUN THE FILE AS A PROGRAM. PERMISSIONS FOR DIRECTORIES: FOR DIRECTORIES,READ PERMISSION ALLOWS USERS TO LIST THE CONTENTS OF THE DIRECTORY,WR...

  1.A LOOP INVOLVES REPEATING SOME PORTION OF THE PROGRAM EITHER A SPECIFIED NO OF TIMES OR UNTIL A PARTICULAR CONDITION IS BEING SATISFIED .THERE ARE THREE METHODS BY WAY OF WHICH WE CAN REPEAT A PART OF A PROGRAM.THERE ARE 1.USING  A WHILE STSTEMENT 2.USING A UNITL STATEMENT 3.USING A FOR STATEMENT 1.WHILE STSTEMENT SYNTAX: WHILE[CONDITION] DO ............................ ........................... ............................ DONE THE STATEMENTS WITHIN THE WHILE LOOP WOULD KEEP ON GETTING EXECUTED TILL THE CONDITION IS TRUE.WHEN THE CONDITION IS FALSE,THE CONTROL TRANSFER TO AFTER DONE STATEMENT.

 1. V1 SP24 ECHO ''ENTER A SINGLE CHARACTER'' READ CH CASE $CH IN [A-Z])ECHO ''YOU ENTERED A SMALL CASE ALPHABET'' .. ,, [A-Z])ECHO''YOU ENTERED A UPPER CASE ALPHABET'' .. ,, [0-9])ECHO''YOU ENTERED A DIGIT'' .. ,, ?)ECHO''YOU ENTERED A SPECIAL CHARACTER'' .. ,, *)ECHO ''YOU ENTERED MORE THAN ONE CHARACTER'' .. ,, ESAC :WQ(SAVE AND QUIT)

 1. VI SP8 ECHO ENTER DIRECTORY NAME READ DNAME IF CD $DNAME THEN ECHO ''CHANGED TO $DNAME'' PWD FI :WQ(SAVE AND QUIT) 2.IF-THEN-ELSE-FI STATEMENT SYNTAX IF CONDITION THEN ------------- ------------- ELSE ------------ ------------ FI THE EXIT STATUS OF THE CONTROL COMMAND IS 0 THEN IT EXECUTES THEN STATEMENTS OTHERWISE IT EXECUTES ELSE STATEMENTS.

 1.SHELL: SHELL IS COMMAND LINE INTERPRETER.IT TAKES COMMANDS FROM USER AND EXECUTES THEM.IT IS AN INTERFACE BETWEEN USER AND KERNEL. THE THREE MOST WIDELY USED UNIX SHELL ARE BOURNE SHELL .KORN SHELL AND C SHELL. SHELL: BOURNE SHELL DEVELOPED BY: STEVE BOURNE SHELL PROMPT: $ EXECUTION COMMAND: SH SHELL: KORN SHELL DEVELOPED BY: DAVID KORN SHELL PROMPT: $ EXECUTION COMMAND: KSH SHELL: C SHELL DEVELOPED BY: BILL JOY,CALIFORNIA UNIVERSITY STUDENT SHELL PROMPT: % EXECUTION COMMAND: CSH EACH SHELL HAS MERITS AND DEMERITS OF ITS OWN,MOREOVER THE SHELL SCRIPTS WRITTEN FOR ONE SHELL MAY NOT WORK WITH THE OTHER SHELL.THIS IS BECAUSE DIFFERENT SHELL USE DIFFERENT MECHANISMS TO EXECUTE THE COMMANDS IN THE SHELL SCRIPT.BOURNE SHELL SINCE IT IS ONE OF THE MOST WIDELY USED UNIX SHELL IN EXISTENCE TODAY. ALMOST ALL UNIX IMPLEMENTATIONS OFFER THE BOURNE SHELL AS PART OF THEIR STANDARD CONFIGURATION.IT IS SMALLER THAN THE OTHER TWO SHELLS AND THEREFORE MORE EFFICIENT FOR MOST SHELL PROCESSING.HOWE...

  1.SHELL: THE SHELL READS YOUR COMMANDS AND INTERPRETS THEM AS REQUESTS TO EXECYE A PROGRAM OR PROGRAMS,WHICH IT THEN ARRANGES TO HAVE CARRIED OUT.BECAUSE THE SHELL PLAYS THIS ROLE,IT IS CALLED A COMMAND INTERPRETER.BESIDES BEING A COMMAND INTERPRETER,THE SHELL IS ALSO A PROGRAMMING LANGUAGE.AS A PROGRAMMING LANGUAGE,IT PERMITS YOU TO CONTROL HOW AND WHEN COMMANDS ARE CARRIED OUT.SHELL ACTS AS AN INTERFACE BETWEEN USER AND THE KERNEL. 2.KERNEL: THE KERNEL IS THE PART OF THE OPERATING SYSTEM THAT INTERACTS DIRECTLY WITH THE HARDWARE OF A COMPUTER,THROUGH DEVICE DRIVERS THAT ARE BUILT INTO THE KERNEL.IT PROVIDES SET OF SERVICES THAT CAN BE USED BY PROGRAMS,INSULATING THESE PROGRAMS FROM THE UNDERLYING HARDWARE.THE MAJOR FUNCTIONS OF THE KERNEL ARE TO MANAGE COMPUTER MEMORY,TO CONTROL ACCESS TO THE COMPUTER,TO MAINTAIN FILE SYSTEM,TO COMPUTER MEMORY,TO CONTROL ACCESS TO THE COMPUTER,TO MAINTAIN FILE SYSTEM,TO HANDLE INTERRUPTS(SIGNALS TO TERMINATE EXECUTION),TO HANDLE ERRORS,TO PERFO...