Operating Systems. Lab Manual. Compiled by: Mr. Mohammed Al-Qadhi Computer Science Department

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1 J A Z A N U N I V E R S I T Y C O M P U T E R S C I E N C E D E P A R T M E N T Operating Systems Lab Manual Compiled by: Mr. Mohammed Al-Qadhi Computer Science Department

2 Table of Contents First Lab Session... 1 What is Linux? UNIX & Linux Operating Systems Linux s File System Terminal Emulators Linux Shell First Keystrokes of Shell Commands... 6 Part One... 8 Interactive Linux Shell Commands Commands for Navigating File System Commands for Manipulating Files and Directories Permissions chmod Change File Mode umask Set Default Permissions Other Commands Part Two Bash Shell Scripting Writing Your First Shell Script What are Shell Scripts? How to Write a Shell Script? Script File Format User Input/Output User Variables Quote Character Control Structures if-then Statement Control Structures if-then-else Statement... 34

3 2.7 Control Structures if-elif-else Statement Command-Controlled Repetition: While Loop List-Controlled Repetition: For Loop Compound Condition Testing Practicing Exercises References Appendix Installing & Operating Cygwin Simulator (Arabic Illustration)... 41

4 Tentative Breakdown of Lab Sessions Topics to be Covered No of Weeks Contact Hours First Lab Session: What is Linux? 1 2 Linux Interactive Shell Commands 5 10 Bash Shell Scripting 6 12

5 P a g e 1 First Lab Session: What is Linux? Lab Objectives: This Lab is for new users of the Linux operating System. The students assumed to have some prior experience with computers, but not necessarily with Linux. The followings are the primary objectives of this lab session: What is Linux? Understanding Linux File System. Knowing different shells in Linux. Knowing Linux terminal. Starting doing some initial shell interactive commands. 1. UNIX & Linux Operating Systems UNIX is a powerful operating system originally developed at AT&T Bell Labs. It is very popular among the scientific, engineering, and academic communities due to its multi-user and multi-tasking environment, flexibility and portability, electronic mail and networking capabilities, and the numerous programming, text processing and scientific utilities available. The UNIX system is mainly composed of three different parts: the kernel, the file system, and the shell. (1) The kernel is that part of the system which manages the resources of whatever computer system it lives on, to keep track of the disks, tapes, printers, terminals, communication lines and any other devices. (2) The file system is the organizing structure for data. The file system is perhaps the most important part of the Linux operating system. The file

6 P a g e 2 system goes beyond being a simple repository for data, and provides the means of organizing the layout of the data storage in complex ways. (3) The shell is the command interpreter. Although the shell is just a utility program, and is not properly a part of the system, it is the part that the user sees. The shell listens to your terminal and translates your requests into actions on the part of the kernel and the many utility programs Linux is a freely available, open source, UNIX-like operating System. Written originally for the PC by Linus Torvalds (A young student in the University of Helsinki), with the help of many other developers across the internet, Linux now runs on multiple hardware platforms, from the smallest to the largest, and serves a wide variety of needs from servers to movie-making to running businesses to user desktops. 2. Linux s File System A file system is a logical organization of storage space designed to contain files in directories. The Linux file system is quite similar to that of MS-DOS or Windows. It is organized hierarchically (inverted tree) into directories for efficient organization. However, in Windows, there are many logical trees represented by drive letters such as C:, D:, H:, etc. In Linux, all file systems (Hard Disks, CD-ROMs, Floppy Disks, ZIP drives, network mounts, etc ) are mounted onto one logical tree. The top of the hierarchy is traditionally called root which is represented by a / (slash).

7 P a g e 3 Figure 1: File System Hierarchy in Linux 3. Terminal Emulators When using a graphical user interface, we need another program called a terminal emulator to interact with the shell. If we look through our desktop menus, we will probably find one. KDE uses konsole and GNOME uses gnome-terminal, though it's likely called simply terminal on our menu. There are a number of other terminal emulators available for Linux, but they all basically do the same thing; give us access to the shell. You will probably develop a preference for one or another based on the number of bells and whistles it has.

8 P a g e 4 Figure 2: Terminal Window in Linux 3.1 Linux Shell When we speak of the command line, we are really referring to the shell. The shell is a program that takes keyboard commands and passes them to the operating system to carry out. Almost all Linux distributions supply a shell program from the GNU Project called bash. The name bash is an acronym for Bourne Again SHell, a reference to the fact bash is an enhanced replacement for sh, the original UNIX shell program written by Steve Bourne. The Shell is somewhat unique, in that it is both a powerful command line interface to the system and a scripting language interpreter. As we will see, most of the things that can be done on the command line can be done in scripts, and most of the things that can be done in scripts can be done on the command line.

9 P a g e 5 The Shell is simply another program on top of the kernel which provides a basic human-os interface. It is a command interpreter that is built on top of the kernel which enables users to run services provided by the UNIX OS. In its simplest form, a series of commands in a file is a shell program that saves having to retype commands to perform common tasks. Figure 3: Linux OS Structure The following UNIX/Linux Shells are more likely to be used: [1] sh: Bourne Shell (Original Shell) (Steven Bourne of AT&T) [2] bash: Bourne Again Shell (GNU Improved Bourne Shell) [3] csh: C-Shell (C-like Syntax)(Bill Joy of Univ. of California) [4] ksh: Korn-Shell (Bourne+some C-shell)(David Korn of AT&T) [5] tcsh: Turbo C-Shell (More User Friendly C-Shell).

10 P a g e 6 4. First Keystrokes of Shell Commands Command date cal df free exit clear history echo $SHELL Function Displays the current time and date. Displays a calendar of the current month. To see the current amount of free space on your disk drives To display the amount of free memory Ending a terminal session Clearing the screen Displays the history of commands that have been entered so far. To check which shell is used recently Note: you can go back to the list of entered commands one-by-one by means of the upward and downward arrows buttons on the keyboard. This is useful and timesaving if one wants to reuse or modify a command that has been entered before instead of rewriting the whole command again.

11 Part One Interactive Linux Shell Commands

12 P a g e 8 Lab Objectives: To make students: Able to use Linux terminal to administrate Linux. Familiar with Linux s Bash Shell interactive commands related to: File system navigation. Manipulating files and directories. Permissions. 1.1 Commands for Navigating File System Command Function Example(s) pwd ls <directory> ls -l ls -lt Displaying The Current Working Directory To list the files and directories in the current working directory To list the files and directories in a specified directory To list the files and directories in a specified directory with revealing more details To list the files and directories in a specified directory with revealing more details [student@localhost ~]$ pwd [student@localhost ~]$ ls [student@localhost ~]$ ls /home/student/mohd [student@localhost ~]$ ls -l [student@localhost ~]$ ls -lt

13 P a g e 9 [student@localhost ~]$ pwd [student@localhost ~]$ ls cd <dir> Changing current directory the working To open mohd directory: [student@localhost ~]$ cd mohd If the directory you want to change to is not within the current working directory then, you should specify the directory path: cd.. cd - tree <options> [directory] Changing the current working directory by going one directory backward Changes the working directory to the previous working directory. Display the contents of a directory in a tree hierarchy format [student@localhost ~]$ cd /<dir path>/mohd [student@localhost ~]$ pwd To go back to student : [student@localhost ~]$ cd.. [student@localhost ~]$ pwd [student@localhost ~]$ cd - [student@localhost ~]$ cd / In the following example, executing the command will display 2 directory levels (relative to the current location) in tree form: [student@localhost ~]$ tree -d -L 2 More options: tree -a: Include hidden files in the tree listing tree -d: List directories only tree -L [NUM]: List the specified number of levels deep

14 P a g e Commands for Manipulating Files and Directories Command Function Examples gedit mkdir <directory name> Creating textual files using gedit program Creating directories [student@localhost ~]$ gedit ahmed.txt [student@localhost ~]$ gedit OS.txt To create a single directory [student@localhost ~]$ mkdir dir1 To create multiple directories at once [student@localhost ~]$ mkdir dir2 dir3 dir4 [student@localhost ~]$ cp ahmed.txt dir1 Copy files and directories from source to dest Note: we here just mentioned the text file and the directory without their full path because; both of them are located in the current working directory. However, if any of them located outside the current working directory then; the full file path should be mentioned as follows: [student@localhost ~]$ cp /<file path>/ahmed.txt /<dir path>/dir1 cp <source> <dest> We can use update option when copying files from one directory to another, only copy files that either don't exist, or are newer than the existing corresponding files, in the destination directory: Using * wildcard to copy a set of files having the same file extension at once [student@localhost ~]$ cp -u *.txt dir2 We can use interactive option before overwriting an existing file, prompt the user for confirmation. If this option is not specified, cp will silently overwrite files: [student@localhost ~]$ cp -i *.txt dir2 We can use verbose option to display informative messages as the copy is performed: [student@localhost ~]$ cp -v *.txt dir2

15 P a g e 11 [student@localhost ~]$ mv ahmed.txt dir1 To move files and folders Note: we here just mentioned the text file and the directory without their full path because; both of them are located in the current working directory. However, if any of them located outside the current working directory then; the full file path should be mentioned as follows: [student@localhost ~]$ mv /<file path>/ahmed.txt mv <source> <dest> We can use update option when moving files from one directory to another, only move files that either don't exist, or are newer than the existing corresponding files, in the destination directory: Using * wildcard to move a set of files having the same file extension at once [student@localhost ~]$ mv -u *.txt dir2 We can use interactive option before overwriting an existing file, prompt the user for confirmation. If this option is not specified, mv will silently overwrite files: [student@localhost ~]$ mv -i *.txt dir2 We can use verbose option to display informative messages as the move is performed: [student@localhost ~]$ mv -v *.txt dir2 student@localhost ~]$ rm ahmed.txt dir1 rm <file> To remove (delete) files and directories: Note: we here just mentioned the text file and the directory without their full path because; both of them are located in the current working directory. However, if any of them located outside the current working directory then; the full file path should be mentioned as follows: [student@localhost ~]$ rm <file path> ahmed.txt

16 P a g e 12 rmdir <directory> To delete directories. We can use interactive option before overwriting an existing file, prompt the user for confirmation. If this option is not specified, rm will silently overwrite files: [student@localhost ~]$ rm -i ahmed.txt We can use verbose option to display informative messages as the removal is performed: [student@localhost ~]$ rm -v ahmed.txt [student@localhost ~]$ rmdir dir1 Note: rmdir will only remove empty directories. If dir1 is a non-empty directory, use: [student@localhost ~]$ rm -r dir1 More Practicing Examples

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18 P a g e Permissions Command Function Examples id To find out information about the current user s identity [student@localhost ~]$ id [student@localhost ~]$ ls l moh.txt ls -l Access rights to files and directories are defined in terms of read access, write access, and execution access. If we look at the output of the ls command, we can get some clue as to how this is implemented: Result of command: -rw-rw-r-- 1 me me :52 moh.txt The first ten characters of the listing are the file attributes. The first of these characters is the file type. Table 1 is listing the file types you are most likely to see. chmod Change file mode See Subsection umask Set Default Permissions See Subsection Table 1: File Types

19 P a g e 15 The remaining nine characters of the file attributes, called the file mode, represent the read, write, and execute permissions for the file's owner, the file's group owner, and everybody else: When set, the r, w, and x mode attributes have the following effect on files and directories: Table 2: Permission Attributes

20 P a g e 16 Table 3: Permission Attribute Examples chmod Change File Mode To change the mode (permissions) of a file or directory, the chmod command is used. Be aware that only the file s owner or the super user can change the mode of a file or directory. chmod supports two distinct ways of specifying mode changes: octal number representation, or symbolic representation. We will cover octal number representation first. With octal notation we use octal numbers to set the pattern of desired permissions. Since each digit in an octal number represents three

21 P a g e 17 binary digits, this maps nicely to the scheme used to store the file mode. This table shows what we mean: Table 4: Permission Possibilities List By using three octal digits, we can set the file mode for the owner, group owner, and world: [student@localhost ~]$ ls -l mohd.txt -rw-rw-r-- 1 me me :52 foo.txt [student@localhost ~]$ chmod 600 mohd.txt [student@localhost ~]$ ls -l mohd.txt -rw me me :52 foo.txt By passing the argument 600, we were able to set the permissions of the owner to read and write while removing all permissions from the group owner and world. Though remembering the octal to binary mapping may seem inconvenient, you will usually only have to use a few common ones: 7 (rwx), 6 (rw-), 5 (r-x), 4 (r--), and 0 (---).

22 P a g e 18 chmod also supports a symbolic notation for specifying file modes. Symbolic notation is divided into three parts: who the change will affect, which operation will be performed, and what permission will be set. To specify who is affected, a combination of the characters u, g, o, and a is used as follows: Table 5: chmod Symbolic Notation If no character is specified, all will be assumed. The operation may be a + indicating that a permission is to be added, a - indicating that a permission is to be taken away, or a = indicating that only the specified permissions are to be applied and that all others are to be removed. Permissions are specified with the r, w, and x characters. Here are some examples of symbolic notation:

23 P a g e 19 Table 6: chmod Symbolic Notation Examples umask Set Default Permissions The umask command controls the default permissions given to a file when it is created. It uses octal notation to express a mask of bits to be removed from a file's mode attributes. Let's take a look: [student@localhost ~]$ rm -f foo.txt [student@localhost ~]$ umask 0002 [student@localhost ~]$ > foo.txt [student@localhost ~]$ ls -l foo.txt -rw-rw-r-- 1 me me :53 foo.txt

24 P a g e 20 We first removed any old copy of foo.txt to make sure we were starting fresh. Next, we ran the umask command without an argument to see the current value. It responded with the value 0002 (the value 0022 is another common default value), which is the octal representation of our mask. We next create a new instance of the file foo.txt and observe its permissions. We can see that both the owner and group both get read and write permission, while everyone else only gets read permission. The reason that world does not have write permission is because of the value of the mask. Let's repeat our example, this time setting the mask ourselves: [student@localhost ~]$ rm foo.txt [student@localhost ~]$ umask 0000 [student@localhost ~]$ > foo.txt [student@localhost ~]$ ls -l foo.txt -rw-rw-rw- 1 me me :58 foo.txt When we set the mask to 0000 (effectively turning it off), we see that the file is now world writable. To understand how this works, we have to look at octal numbers again. If we take the mask and expand it into binary, then compare it to the attributes we can see what happens: Ignore for the moment the leading zeros (we'll get to those in a minute) and observe that where the 1 appears in our mask, an attribute was removed in this case, the world write permission. That's what the mask does. Everywhere a 1 appears in the binary value of the mask, an attribute is unset. If we look at a mask value of 0022, we can see what it does:

25 P a g e 21 Again, where a 1 appears in the binary value, the corresponding attribute is unset. Play with some values (try some sevens) to get used to how this works. When you're done, remember to clean up: [student@localhost ~]$ rm foo.txt; umask 0002 Most of the time you won't have to change the mask; the default provided by your distribution will be fine. In some high-security situations, however, you will want to control it.

26 P a g e Other Commands Command Function Examples Online manual [student@localhost ~]$ man ls for shell man <command> commands [student@localhost ~]$ man pwd whatis <command> locate <options> <directory/file> Display a description of the specified command Search the locate database for files and directories. [student@localhost ~]$ whatis ls [student@localhost ~]$ whatis ls who rm [student@localhost ~]$ locate moh > The output of a command can be redirected to other locations such as a text file. Redirection is initiated by using the > character on the keyboard. [student@localhost ~]$ [student@localhost ~]$ date > date.txt ls -l testfile touch <options> <file> Update time stamps on a file. [student@localhost ~]$ [student@localhost ~]$ touch testfile ls -l testfile cat <file> expr <expression> Displays the content of a file on the command line. [student@localhost ~]$ [student@localhost ~]$ date cat mohd.txt The expr command allowed the processing of equations from the command line, [student@localhost ~]$ expr

27 P a g e 23 While the standard operators work fine in the expr command, the problem comes in actually using them from a script or the command line. Many of the expr command operators have other meanings in the shell (such as the asterisk). Using them in the expr command produces odd results: [student@localhost ~]$ expr 5 * 2 expr: syntax error Table 7: Some of the expr Command Operators

28 Part Two Bash Shell Scripting

29 P a g e 25 Lab Objectives: To make students: Able to write simple shell scripts to illustrate programming logic that contains entering/ printing data, control structures. Able to write simple shell scripts that uses repetition concept. Feel how much similarity that shell scripting has in compare to other programming languages. 2.1 Writing Your First Shell Script What are Shell Scripts? In the simplest terms, a shell script is a file containing a series of commands. The shell reads this file and carries out the commands as though they have been entered directly on the command line How to Write a Shell Script? To successfully create and run a shell script, we need to do three things: 1) Write a script. Shell scripts are ordinary text files. So we need a text editor to write them. The best text editors will provide syntax highlighting, allowing us to see a color-coded view of the elements of the script. Syntax highlighting will help us spot certain kinds of common errors. vim, gedit, kate, and many other editors are good candidates for writing scripts.

30 P a g e 26 2) Make the script executable. The system is rather fussy about not letting any old text file be treated as a program, and for good reason! We need to set the script file s permissions to allow execution. 3) Put the script somewhere the shell can find it. The shell automatically searches certain directories for executable files when no explicit pathname is specified. For maximum convenience, we will place our scripts in these directories Script File Format In keeping with programming tradition, we ll create a hello world program to demonstrate an extremely simple script. So let s fire up our text editors and enter the following script: #!/bin/bash # This is our first script. echo 'Hello World!' The last line of our script is pretty familiar, just an echo command with a string argument. The second line is also familiar. It looks like a comment that we have seen used in many of the configuration files we have examined and edited. One thing about comments in shell scripts is that they may also appear at the end of lines, like so: echo 'Hello World!' # This is a comment too

31 P a g e 27 Everything from the # symbol onward on the line is ignored. Like many things, this works on the command line, too: [student@localhost ~]$ echo 'Hello World!' # This is a comment too Hello World! Though comments are of little use on the command line, they will work. The first line of our script is a little mysterious. It looks like it should be a comment, since it starts with #, but it looks too purposeful to be just that. The #! character sequence is, in fact, a special construct called a shebang. The shebang is used to tell the system the name of the interpreter that should be used to execute the script that follows. Every shell script should include this as its first line. Now, let s begin implementing the 3-steps procedure: 1) Write this script using the window-based gedit text editor as following: [student@localhost ~]$ gedit hello_world The following window in figure 3 will be opened:

32 P a g e 28 Figure 3: gedit program window in Linux After saving the file, it means that it has been saved within the current working directory. 2) Make the script executable by means of chmod command: [student@localhost ~]$ chmod u+x hello_world 3) Run the shell script from the command line using the following method: [student@localhost ~]$./hello_world

33 P a g e User Input/Output Construct(s) [1] echo: command is well appreciated when trying to debug scripts. Example 1 Example 2 Example 3 Example 4 Syntax : echo {options} string Options: -n : do not output a new-line at the end. String can be a weakly quoted or a strongly quoted string. In the weakly quoted strings, the references to variables are replaced by the value of those variables before the output. [2] read: shell allows to prompt for user input Syntax: read varname [more vars] or read p "prompt" varname [more vars] words entered by user are assigned to varname and more vars last variable gets rest of input line #!/bin/bash # This is a comment! echo Hello World # This is a comment, too! #!/bin/bash # This is a comment! echo "Hello World" # This is a comment, too! #!/bin/bash echo Who am I talking to? read user_name echo Hello $user_name #!/bin/bash read -p "enter your name: " first echo "First name: $first" echo "Last name: $last" last

34 P a g e User Variables Construct(s) Setting variables allows you to temporarily store data and use it throughout the script, making the shell script more Example 1 Example 2 like a real computer program. Variables Naming Rules User variables can be any text string of up to 20 letters, digits, or an underscore character. User variables are case sensitive, so the variable Var1 is different from the variable var1. Values are assigned to user variables using an equal sign. No spaces can appear between the variable, the equal sign, and the value. For example: var1=10 var2=-57 var3=testing var4="still more testing" The shell script automatically determines the data type used for the variable value. #!/bin/bash # testing variables GPA= 4 student="ahmed" echo "$student has average of = $GPA" GPA= 2 student="ali" echo "$student has average of = $GPA" #!/bin/bash # assigning a variable value to another variable value1=10 value2=$value1 echo The resulting value is $value2

35 P a g e Quote Character Construct(s) There are three different quote characters with different behaviour. These are: [1] : double quote, weak quote. If a string is enclosed in the references to variables (i.e $variable ) are replaced by their values. Also, back-quote and escape \ characters are treated specially. [2] : single quote, strong quote. Everything inside single quotes are taken literally, nothing is treated as special. [3] ` : back quote (aka backtick). A string enclosed as Example 1 Example 2 Example 3 such is treated as a command and the shell attempts to execute it. If the execution is successful the primary output from the command replaces the string. #!/bin/bash # printing variable value using double and single quotes GPA= 4 student="ahmed" echo "$student has average of = $GPA" # true echo $student has average of = $GPA # false #!/bin/bash # using the backtick character testing=`date` echo "The date and time are: " $testing #!/bin/bash # An example of using the expr command var1=10 var2=20 var3=`expr $var2 / $var1` echo The result is $var3

36 P a g e 32 Meaning Numeric String Greater than Greater than or equal Less than Less than or equal -gt -ge -lt -le Equal -eq = or == Not equal -ne!= str1 is less than str2 str1 is greater str2 String length is greater than zero String length is zero str1 < str2 str1 > str2 -n str -z str Table 8: Relational Operators for comparing both numeric and strings

37 P a g e Control Structures if-then Statement Construct(s) Syntax : if [ condition ] then statements fi statements are executed only if the condition succeeds, i.e. has return status 0 Example 1 Example 2 #!/bin/bash # testing the if statement if date then echo "it worked" fi #!/bin/bash read p enter any number num if [ num -ge 0 ] then echo >=0 fi

38 P a g e Control Structures if-then-else Statement Construct(s) Syntax : if [ condition ] then statements-1 else statements-2 fi executes statements-1 if condition is true executes statements-2 if condition is false Example 1 Exercise #!/bin/bash # using numeric test comparisons val1=10 val2=11 if [ $val1 -eq $val2 ] then echo "The values are equal" else echo "The values are different" fi Write a bash shell script that will enter the age of a person and whether he has a pension or not to check whether he deserves a social insurance or not based on the following formula: If person s age is greater than or equal 60 years and does not have pension then, he can get social insurance. Otherwise, he cannot get social insurance.

39 P a g e Control Structures if-elif-else Statement Construct(s) Syntax : if [ condition ] then statements-1 elif [ condition ] then statement-2 else statements-3 fi The word elif stands for else if It is part of the if statement and cannot be used by itself Example 1 Exercise #!/bin/bash # comparison between three entered numbers read -p enter any number: n if [ n -gt 0 ]; then echo the number is +ve elif [ n -lt 0 ]; then echo the number is -ve else echo the number is zero fi Write a bash shell script that will enter the year number of a student and decide whether he is: freshman : for year=1, sophomore for year=2, junior for year=3 or senior for year=3.

40 P a g e Command-Controlled Repetition: While Loop Construct(s) Purpose: to execute commands in command-list as long as expression evaluates to true Syntax : while [ expression ] do command-list done Example 1 Example 2 Exercise #!/bin/bash stat=hello while [ "$stat"!= "bye" ] do echo "Please type something in (bye to quit)" read stat echo "You typed: $stat" done #!/bin/bash # calculating the sum of numbers from 1 to 20 num=1 sum=0 while [ $num le 20 ] do let sum=$sum+$num let num=$num+1 done Write a bash shell script that will enter the marks of 5 students and calculate their average using While-loop.

41 P a g e List-Controlled Repetition: For Loop Construct(s) Purpose: Example 1 Example 2 To execute commands as many times as the number of words in the argument-list Syntax : for variable in {argument-list} do done #!/bin/bash commands for i in do echo $i done #!/bin/bash # compute the average weekly temperature sum=0 for day in Sat Sun Mon Tue Wed Thu Fri do read p enter the temperature of $day temp let sum = $sum+$temp if [ $temp ge 25 ]; then echo $day is hot else echo $day is cold fi done let avg = $sum/7 echo average= $avg

42 2.10 Compound Condition Testing P a g e 38 Construct(s) Example 1 Example 2 Exercise There are two Boolean operators for compound conditions: AND: Both conditions must be met for the then section to execute. Syntax: [ condition1 ] && [ condition2 ] OR: If either condition evaluates to a true condition, the then section is executed. Syntax: [ condition1 ] [ condition2 ] #!/bin/bash # finding the maximum among three entered numbers read -p enter three numbers num1 num2 num3 if [ $num1 gt $num2 ] && [ $num1 gt $num3 ] ; then echo num1=$num1 is the maximum elif [ $num2 gt $num1 ] && [ $num2 gt $num3 ] ; then echo num2=$num2 is the maximum else echo num3=$num3 is the maximum fi #!/bin/bash # calculating the sum of odd numbers from 1 to 20 num=1 sum=0 rem=`expr $num % 2` while [ $num le 20 ] && [ $rem ne 1 ] do let sum=$sum+$num let num=$num+1 rem=`expr $num % 2` done Write a bash shell script that will enter the age of a person and whether he has a pension or not to check whether he deserves a social insurance or not based on the following formula: If person s age is greater than or equal 60 years and does not have pension then, he can get social insurance. Otherwise, he cannot get social insurance.

43 P a g e Practicing Exercises [1] Write a bash shell script that will enter a number from the keyboard and find whether it is a perfect number or not. Hint: a perfect number is one whose sum of its proper divisors except the number itself, is equal to the number itself. For instance, the divisors of 6 are 1, 2, 3 and the 1+2+3=6, therefore 6 is a perfect number. [2] Write a bash shell script that will classify the even and odd numbers between 1 and 20 by printing each number with specifying whether it is even or odd on the terminal. [3] Write a bash shell script that will find and print only the prime numbers between 1 and 30. [4] Use the concept of looping to write a bash shell script that will enter the final marks of a set of 10 students in operating systems lab class. Also, it should perform the following: Print the grade of each student which will be one of the set: {A+,A,B+,B,C+,C,D+,D,F} based on Jazan University grading system. Calculates the average mark of the class. Counts how many student got F grade.

44 P a g e 40 References [1] Nicholas Marsh Introduction to the Command Line: The Fat Free Guide to Unix and Linux Commands (2nd ed.). CreateSpace, Paramount, CA. [2] William E. Shotts, Jr Linux Command Line: A Complete Introduction No Starch Press, CA. [3] Richard Blum and Christine Bresnahan Linux Command Line and Shell Scripting Bible, Second Edition (2nd ed.). Wiley Publishing.

45 P a g e 41 Appendix Cygwin Bash Shell Scripting Cygwin Shell Commands Finish 4

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50 P a g e 46 nano (nano prog) gedit prog

51 P a g e 47 nano nano y x Ctrl enter