Solutions to Chapter One Questions 1. Why does a computer require an operating system? Ans.
A computer requires an operating system to control the various hardware devices and manage its own resources. The operating system also allows users to create and manage files and run various applications. The operating system performs the following basic tasks: 1. 2. 3. 4. 5.
Peri Periph pher eral al Man Manag agem emen entt Memo Memory ry Mana Manag gemen ementt Proc Proces ess s Mana Manage gem ment ent File Filesy syst stem em Man Manag agem emen entt Comm Comman and d Inter Interpr pret etat atio ion n
2. How is UNIX different from other operating systems? Ans.
The differences between UNIX and other operating systems are:
UNIX is a multi-user operating system. Unlike DOS and Windows, a number of users can access the UNIX operating system simultaneously. UNIX has better scalability than Windows OS. UNIX is stable and can be operated continuously without being rebooted compared to Windows OS.
3. What is the function of the UNIX kernel? Ans.
The kernel, collection of programs written in C l anguage, is the core of the UNIX operating system. The kernel manages the hardware and the executing processes. The kernel acts as an in terface between the applications and the system hardware. The application programs communicate with the hardware by using the services of the kernel.
4. What is the meaning of multitasking? Ans.
A multitasking operating system allows a computer to run several programs at the same time. The multitasking operating system divides the CPU time among various processes and gives an impression of doing many tasks at the same time. The concept of dividing CPU time is known as ti me-sharing.
5. What is the importance of a user name and a password? Ans.
A user needs to logon with the user name and password in order to start a UNIX session on a system. The user name, which is also known as login name or login, and the password are provided by the system administrator. If a user does not type his user name and password or types them incorrect, the system does not starts the session.
.
Solutions to Chapter Two Questions 1. How are commands located in Unix? Ans.
The commands can be located using the type command in Unix.
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2. How does the type command work? Ans.
The type command returns the location of the command that is passed as a parameter to the type command. For example, $ type who When the above command is entered, the shell searches for the command in the search path specified in the PATH environmental variable. If the command is found, the command's location is displayed on the console.
3. How do you find out whether a command is internal or external? Ans.
The commands that are built into the shell are called internal commands. For example, the cd command. The shell does not start any separate process to run the internal commands. The commands for which executable files are stored in some other directory rather then in shell itself are called external commands. For example, the cat command. The cat command is an external program stored in the / bin/cat file. The shell starts a new subprocess to execute an external command.
4. What is a secondary prompt? Ans.
Sometimes, a command to be executed is lengthy and you need to split it in several lines. The Unix shell displays a second prompt to accept the incomplete command. By default, the second prompt is displayed as > symbol.
5. How do you stop and resume the scrolling of the screen display? Ans.
You can stop scrolling of the screen display by pressing CTRL-s and resume scrolling by pressing CTRL-q keys from the keyboard.
6. How do you get one-line descriptions of any command in Unix? Ans.
You can get one-line description of any command by using the whatis command in Unix. For example, to see the one-line description of cat command, you specify the following command: $ whatis cat
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Solutions to Chapter Three Questions 1. Use the cal command to find out whether the year 1900 was a leap year. Ans.
The following command can be used to find whether the year 1900 is a leap year or not: $ cal 2 1900 As the output is showing 28 days in February, 1900 was not a leap year.
2. Use the echo command to display the message 'Good Morning'. The cursor should move to the next line after
displaying the message. Ans.
The command to display 'Good Morning' using the echo command is: $ echo "Good Morning" 3. Display the current date in the mm/dd/yy format. Ans.
The command to display current date in mm/dd/yy format is: $ date +"%D"
4. Use bc to divide 35 by 9. Set the scale to 2. Ans.
The following command is given for using the bc: $ bc scale=2 35/9
5. Record your login session into a file. Ans.
The following command is given to record the login session into a file: $ script
6. List out the users logged on into the system. Ans.
The command to list the current users is: $ who
7. Display your terminal filename. Ans.
The command to display the terminal file name is: $ tty
8. Display the release version of your operating system.
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Ans.
The command to display the release version of the operating system is: $ uname -r
9. How do you check a file for spelling errors? Ans.
A file can be checked for spelling errors by using the ispell command.
10. How do you lock your terminal for 20 minutes? Ans.
The command to lock the terminal for 20 minutes is: lock -20 11. How do you check your terminal settings? Ans.
You can check your terminal settings using the stty command. Solutions to Chapter Four Questions 1. What are the rules to b e followed while naming files in Unix? Ans.
The rules to be followed while naming files in Unix are: a
The filename filename in Unix Unix can be a combinatio combination n of upper case case letters, letters, lower lower case letters letters,, numbers, numbers, a period period (.), comma comma (,), (,), or underscore (_).
b
The filenam filename e should should not not contain contain &, *, \, |, (, ), [,[, ], {, }, }, $, <, >, ?, ',', ", /, ;, ^, !, %, %, ~, `, and #.
c
The Unix Unix comm command and names names shou should ld not not be used used as filena filenames mes..
2. Which of the following file names are not valid and Why?
a.
Books
b.
file?
c.
cat
d.
file name
e.
book.lst
f.
rank*
g.
slno# Ans.
The invalid filenames are: b.
file?: Presence of ?.
c.
cat: command name.
d.
file name: Presence of space.
f.
rank*: Presence of *.
g.
slno#: Presence of #.
3. Suppose the working directory is user1 and the parent is user, what is the absolute pathname of the file list.txt in the
working directory user1. Ans.
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The absolute pathname of the file list.txt is: /user/user1/list.txt
4. What are the different types of files in Unix? Ans.
Different types of files in Unix are ordinary files, directory files, special files, and linked files.
5. Why is the size of a directory file small? Ans.
The size of a directory file i s small because a directory file contains the name and the i-number of each item (file or subdirectory) contained within the directory. 6. Create a new directory in your home directory and change to it. display the absolute path. Ans.
The command to create a new diretory is: $ mkdir mydir The command to change to the new directory is: $ cd mydir The command to display the absolute path is: $ pwd
7. Can a directory be removed if it is not empty? Ans.
No, a directory must be empty, if you want to delete it.
8. What are hidden files and how can they be displayed? Ans.
The files whose name begin with a d ot (.) character is known as hidden file. The system files, usually, are hidden files. You can display hidden files using the ls -a or ls -A commands.
` Solutions to Chapter Five Questions 1. Create a file called lesson1 in your home directory using the cat command. Ans.
The command to create the file, lesson1 is: $ cat > lesson1 This is a sample file. +D
2. Create a directory called lessons and copy the file lesson1 to this directory. Ans.
The command to create a directory is: $ mkdir lessons The command to copy the file, lesson1 to the directory, lessons is: $ cp lesson1 lessons
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3. Remove the file lesson1 from the home directory. Ans.
The command to remove the file, lesson1 from the h ome directory is: $ rm lesson1
4. Create another file called lesson2 and move it to the directory lessons. Ans.
The command to create the file, lesson2 is: $ cat > lesson2 This is another sample file. +D The command to move the file, lesson2 to t he directory, lessons is: $ mv lesson2 lessons 5. Change to the directory, lessons, and count the number of characters and lines in the files lesson1 and lesson2. Ans.
The command to change to the directory, lessons is: $ cd lessons The command to counting the number of lines and characters in both the files is: $ wc -cl lesson1 lesson2
6. What happens when lesson1 and lesson2 are compared? Ans.
When the lesson1 and lesson2 files are compared using the cmp command, the system displays no result, i f the content of the files are same. If the content of the files are different, then the byte and line number are displayed where the first difference occurs.
7. List the contents of th e directory lessons datewise. Ans.
The command to list the content of the directory lessons datewise is: $ ls -lt
8. Create a file with at least 100 bytes and split it into files of 20 bytes each. Ans.
The command to create a file, myfile is: $ cat > myfile A dangling symbolic link is a symbolic linked file, whose source file has been deleted. For example, if you delete the sample.txt file from your system, the samplelnk.txt will become a dangling l ink. +D The command to split myfile into files o f 20 bytes each is: $ split -b 20 myfile mfile Solutions to Chapter Six Questions 1. How do you list all th e attributes of a file in your home directory?
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Ans.
The command to list the attributes of a file in a home directory are: $ ls -l
2. Create a file called sample.txt. How do you assign all permissions to the owner, read and write permissions to the
group, and no permissions to others using relative permissions and absolute permissions? Ans.
The command to create the sample.txt file is: $ cat > sample.txt The command to assign the permissions using relative permissions is: $ chmod u+rwx,g+rw,o-rwx sample.txt The command to assign the permissions using absolute permissions is: $ chmod 760 sample.txt
3. What happens if a directory has permissions 777? Ans.
If a directory has 777 permissions, all the users have read, write, and execute permissions on that particular directory. They can add, delete, or modify any file present in that directory. 4. How are default file and directory permissions changed? Ans.
The default file and directory permissions can be changed using the umask command. For example, umask 022 The above command sets the following permissions on a newly created files:
Read and Write permissions for file owner.
Read permission for group owner.
Read permission for other users.
5. What are the changes seen in the file's inode number when a link is created? Ans.
When a link of a fi le is created, the inode number of the existing file is assigned to t he new created linked file. Both linked files will have the same inode number. 6. How are inode numbers displayed? If two files have the same inode numbers, what do you conclude? What happens
when you delete one of these fi les? Ans.
The inode numbers of the files can b e displayed using ls -il command. Same inode number of two files indicates that the files are linked files. If a linked file is deleted, the second file still remains and is not deleted from the system.
7. How are hard links created? Ans.
The hard links are created using the ln command. 8. What are the uses of hard links? Ans.
The uses of hard links are:
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a.
Hard Hard links links preve prevent nt accid accident ental al delet deletion ion of of files. files.
b.
Hard links links can can make the files files availabl available e to the users, users, when files files in a directory directory are are shifted shifted to another another directory directory..
9. For the file sample.txt, create a symbolic link. What is a dangling symbolic link? Ans.
The command to create a symbolic link for the file, sample.txt is: $ ln -s sample.txt samplelnk.txt A dangling symbolic link is a symbolic linked file, whose source file, to which symbolic linked file is linked, has been deleted. For example, if you delete t he sample.txt file from your system, the samplelnk.txt will b ecome a dangling link. 10. How do you order the list of files by their modification time? Ans.
The command to list the files based on their modification time is: $ ls -t 11. Find all the directories in the /usr directory? Ans.
The command to find all the directories in the /usr directory is: find /usr -type d -print
12. Find all the files having the same inode number in the /usr directory? Ans.
The command to find the files having same inode number in the /usr directory is: find /usr -inum
13. Find all the files called core in your home directory and remove it? Ans.
The command to finding the files called core in your home directory and removing it is: find $HOME -name core -exec rm {} \;
Solutions to Chapter Seven Questions 1. How do you do the following using vi:
a.
delete a line
b.
overwrite te text
c.
move move the the cur curso sorr four four line lines s dow down n
d.
add add a new new line line abov above e a lin line e of of text text
e
remove remove two two lines lines from from the the end end of a text text and add add it to the the beginn beginning ing of of the file file
f.
open open a file file and and move move to the the fifte fifteent enth h line line in in the the file file Ans.
a.
dd
b.
R
c.
4j
d.
O
e.
Keep the the cursor cursor at the second second last line line and in the the escape escape mode press press 2Y, press press 1G, and and press P.
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f.
Type Type vi > at the the shell shell promp prompt, t, press press 15G 15G in the the escape escape mode mode..
2. What are the different ways of adding text using vi? Ans.
Using vi, you can add text in a file using the following commands: a.
i
b.
a
c.
I
d.
A
e.
o
f.
O
3. How do you replace all the occurrences of the word printf with fprintf in a file? Ans.
The following command needs to be given in the vi vi editor in escape mode to replace the word printf :1, $s/printf/fprintf/gp
4. What are the different ways of coming out of vi after saving the file? Ans.
There are three different ways to quit vi after saving the file: a.
:wq
b.
:x
c.
ZZ 5. How do you yank and paste lines? Ans.
To yank and paste the lines, perform the following steps: a.
Keep Keep the curso cursorr at the the line line you you want want to to copy. copy.
b.
Press Press Y or Y, Y, where where n is the total total number number of lines that you you want want to copy. copy.
c.
Place Place the curso cursorr at the the line, where you want want to paste paste the the copied copied lines. lines.
d.
Press Press p to paste paste the line line after after the cursor cursor or or press P to paste paste the lines lines before before the cursor cursor..
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with fprintf in a file:
Solutions to Chapter Eight Questions 1. What are the file d escriptor for standard out, standard in, and standard error? Ans.
The file descriptor for standard out, standard in, and standard error are 1, 0, and 2 respectively.
2. Explain the command: cat>out.dat. Ans.
When you type the command cat>out.dat on the prompt, it waits for the standard input to be entered. Instead of d isplaying the standard input on the monitor, it redirects the output to the file, out.dat.
3. Write a command to pipe the output of cat into the more command. Ans.
$ cat | more
4. Write a command to append the file txt1 to the end of the file txt2. Ans.
$ cat txt1 >> txt2
5. What does the character \ mean to the shell? Ans.
The \ (escape) character is used to specify that the character, written after it, does not have any special meaning. The character that follows the escape character should be displayed as literal. F or example, $ echo \* The above command will display * on the standard output device. 6. How can you remove a file named ?ops without removing the file wops? Ans.
$ rm [^w]ops
7. How do you display the value of the shell variable PATH? What is the variable used for? Ans.
The command to display the value of PATH variable is: $ echo $PATH The PATH variable specifies the directories to be searched for the executable files, when a command needs to be executed.
8. How do you find out the number of users logged in to the system? Ans.
The command to find the number of users logged into the system is: $ who | wc -l Solutions to Chapter Nine Questions 1. What command will give you a listing of all running processes that are owned by you? Ans.
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The command to listing all the running processes is: $ ps
2. What is the name and PID of your shell process? Ans.
Execute the ps command and note the name and PID of your shell process. For example, $ ps PID TTY
TIME CMD
2568 pts/2
00:00:01 bash
17942 pts/2
00:00:00 cat
18384 pts/2
00:00:00 ps
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3. How can you tell if a process is linked to a terminal? Ans.
You can use the ps command with -e option to know whether a process is linked to a terminal or not. The processes that are not linked to any terminal contain ? in the terminal column.
4. How do you run a process in the background? Ans.
To run a process in the background, you need to append & symbol to the command. For example, $ wc Report & The above command will count the characters, words, and lines in t he Report file in the b ackground.
5. How can you terminate a running process? Ans.
You can terminate a running process by using the kill command. With the kill command, you need to specify the PID of the process that you want to terminate.
6. Open another terminal session. Find the pid of this process and kill it. What command did you use? Ans.
1. 2. 3.
Start another another termina terminall session session by logging logging in as a different different user. Use ps ps -aux -aux comm command and to to see the pid pid of the the proce process. ss. Use kill kill -9 comma command nd to to kill kill the the proc process ess..
7. What is the significance of -9 in the command: kill -9 pid? Ans.
The -9 option of the kill command is used to kill the process forcefully because some processes ignore the kill signal.
8. What is a daemon process? Ans.
The processes that are not associated with any terminal are called daemon processes.
9. How do you kill a process running in th e background? Ans.
You can kill the process running in the background using the kill command. You need to specify the PID with the kill command. The status of the background process can be checked using the ps command.
10. What does the following crontab entry mean?
30 15 * * * sort file1.lst > file1.srt Ans.
In the above command, 30 represent minutes and 15 represents hours. The whole command means that everyday at 3:30 PM, the content of file1.lst will be sorted and saved in the file, file1.srt.
Solutions to Chapter Ten Questions
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1. What is the difference between write and talk commands? Ans.
The write command copies the text from one user terminal to the terminal of another user who is also logged on the Unix operating system. The recipient can reply the sender by writing on his terminal and communication starts between the two users. The communication continues until an end-of-file is read from the terminal or an interrupt is sent. The talk command is a visual communication program that copies lines from a user terminal to the terminal of another user. The talk command splits the user terminal into two sections. The upper section is used by the sender to write messages and the lower section displays the received messages.
2. If a user is logged into more than one terminal, how do you send the user a message using write? Ans.
If a user is logged into more than one terminal, the ttyname is used to indicate the appropriate terminal. 3. Find a user who has an account on the system and send a message using mailx? Ans.
The command to find a user who can send a message using mailx is: who -T
4. What happens if you type q at the mailx prompt? Ans.
Typing q at the mailx prompt enables you t o quit the mailx.
5. Where is a user's personal mailbox located? Ans.
A user's personal mailbox is located in the user's home directory.
6. Using the redirection operator on the command line, mail the file mesg.txt to user 1. Ans.
The command to mail the file mesg.txt to user1is: mailx user1 < mesg.txt
exercise no. 6. 7. Include the subject 'my message' in the command line, in exercise Ans.
The command to mail the file mesg.txt to user1 with the subject 'my message'is: mailx -s "my message" user1 < mesg.txt
8. How is pine different from mailx? Ans.
The mailx is a command line tool that is used to send or receive messages at the shell prompt. In the sending mode, mailx runs in an interactive mode and asks for the subject and message to be sent to the receiver. The pine is a character-based menu driven mailer that also provides an address box to maintain the mail addresses list. The incoming and outgoing messages are stored in different folders. The pine main menu window displays various options, such as viewing help on pine, composing a new message, creating address book, and configuring pine.
9. How do you create an address book using pine? Ans.
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To create an address book using pine, you need to press the key 'A' to enter the address book, while the pine main menu window is displayed.
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10. Send a mail to user1 using pine. Ans.
The steps to send a mail using pine are: 4. 5. 6. 7. 8. 9. 10.
Type Type pine pine at the the she shellll prom prompt pt Press Press the the key key C to comp compose ose and send send a mess message age.. Type Type the mail mail addre address ss of user user1 1 in the line line labe labeled led as 'To' 'To' . Type the subject subject of your your mail mail in in the line labeled labeled as 'Subject'. 'Subject'. Type Type your your mes messag sage e in the the Mess Message age Text Text area. area. Pres Press s CTRL CTRL+X +X to to send send the the mes messa sage ge.. Press 'Y' 'Y' at the confirm confirmation ation to send send the message message to to user1. user1.
Solutions to Chapter Eleven Questions 1. Use head and tail to select lines 5 to 10 of a file. Ans.
The command to display the lines 5-10 of a file is: $ tail +5 | head -n 6
2. Generate a code list by selecting departments from emp.lst. Ans.
The command to select departments from the emp.lst file i s: $ cut -d \| -f 3 emp.lst In the above command, 3 represents the column number of the department field of the emp.lst file . Note: The content of the emp.lst file is given in the chapter.
3. Remove the repeated lines from a file. Ans.
The command to remove the repeated lines from a file is: sort | uniq -
4. Convert the content of the file emp.lst to uppercase. Ans.
The command to convert the content of the file emp.lst to upper case is: $ tr '[a-z]' '[A-Z]' < emp.lst
number of times the character character occurs in a file? 5. How will you find out the number Ans.
$ cat | grep -o "?" | wc -l
6. Mail a sorted list of users currently logged in to root, ta king account of the possibility that a user may be logged in more than once. Ans.
$ who | sort | uniq -u > userlist $ mail root < userlist
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Solutions to Chapter Twelve Questions 1. Define each of the following terms;
Shell script, comment, subshell Child process, positional parameter, selection structure Default case, repetition structure, iteration loop Ans.
Shell script: Is a script or program written for the shell of a UNIX. The name of the file can
later be used to execute the stored sequence with a single command. In MS-DOS, these files are known as "batch files", which are recognized by the .bat file name extension. In UNIX, they are called "shell scripts" and do not require special file name extension. Comment: A comment is a part of a source code that explains the working of a code. Comments are ignored by compilers and interpreters. A comment in a PostScript is the text, which is preceded by a '%' sign. The comment in which '%!' is included as the first two characters marks the file as a PostScript code. Subshell: The shell is a utility so you can execute the shell command, such as sh for the Bash shell, to create another shell. This new shell is known as the subshell or the child shell of the current shell. The shell creates a child shell, sub-shell, to execute a shell script. This is done so that the current shell is not affected by the script. The shell script is passed to the child shell for execution. The new shell that is created is terminated as soon as the script running on it completes execution. Child process: A child process is a computer process, which is created by an existing process. The existing process is called the parent process. process. Positional parameter : A positional parameter is a subroutine parameter identified by the
order in which it is listed. Positional parameters are enclosed in parentheses and are separated by commas in a subroutine call. Positional parameters are listed in the order in which they appear in the corresponding subroutine definition.
Selection structure: The selection structure gives a choice to choose one options based
on a condition from a set of options. For example, if-else and case construct. Default case: In a case statement, the default case enables you to specify the code to be executed when the expression does not match any of the specified cases. The default case corresponds to an unrecognized case. Repetition structure: The repetition structure is used for carrying out commands more than once. For example, for, while, and until.
Iteration: Iteration refers to the use of a loop to repeat one or more actions.
Loop: Loop refers to the executable statements repeated a several times in a program,
such as DO-loop, an IF-statement.
2. Develop a script logic that allows only kumar and sachin (login names) to execute a program. Ans.
#!/bin/sh # Allow kumar and sachin to execute a program u=`whoami` if test $u == "kumar" -o $u == "sachin" then set `date` echo "Remember for today" case $1 in Mon) echo "Plan the week.";; Tue) echo "Take clothes to the cleaners.";; Wed) echo " Attend group meeting.";; Thu) echo "Make plans for the weekend.";
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echo "Pick up the clothes from the cleaners.";; Fri) echo "Answer e-mail.";; Sat) echo "You should not be here working."; Echo "Finish your work and log off.";; Sun) echo "Call Grandma and Grandpa.";; esac else echo "You are not allowed to run this script." fi
3. Develop a script logic that executes script only f rom terminal tty01 and tty02. Ans.
#!/bin/sh # Allows script to be executed from terminal tty01 and tty02 u=`tty` if test $u == "tty01" -o $u == "tty02" then set `date` echo "Remember for today" case $1 in Mon) echo "Plan the week.";; Tue) echo "Take clothes to the cleaners.";; Wed) echo " Attend group meeting.";; Thu) echo "Make plans for the weekend."; echo "Pick up the clothes from the cleaners.";; Fri) echo "Answer e-mail.";; Sat) echo "You should not be here working."; echo "Finish your work and log off.";; Sun) echo "Call Grandma and Grandpa.";; esac else echo "The script cannot be executed on this terminal." fi
4. Write a shell script that accepts one or more filenames as arguments, and converts them all to uppercase provided they
exist in the current directory. Ans.
#!/bin/sh # Translating files into uppercase i=1 for name in $* do if test -f $name
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then echo "$name in upper case:" a=`echo $name | tr "[a-z]" "[A-Z]"` mv $name $a else echo "File does not exist." fi done
5. Write a shell script that accepts two directory names, foo1 and foo2, and deletes tho se files in foo2 which are identical
to their namesakes in foo1. Ans.
#!/bin/sh #Deleting identical files from a directory echo "Enter two directories" read d1 read d2 if test ! -d $d1 -o ! -d $d2 then echo "You have entered wrong directory names" else for name in `ls $d2` do for na in `ls $d1` do if test $name == $na then z='y' break else z='n' fi done if test $z != 'n' then echo "Deleting $name" rm $d2/$name else echo "$name does not match with any file i n $d1" fi done fi
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6. Write a shell script that lists files by modification time when called with lm and by access time called with la. By default,
the script should show the listing of all files in the current directory. Ans.
#!/bin/sh # Listing files by modification time and access time s=$1 if test "$s" == "lm" then ls -lt elif test "$s" == "la" then ls -lu else ls -l fi
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7. Write a shell script to d isplay the processes in the system every 30 seconds five times using a (i) while loop (ii) for loop. Ans.
(i) The shell script using the while l oop is: #!/bin/sh # Displaying current processes in the system every 30 seconds i=0 while test $i -lt 5 do ps sleep 30 i=`expr $i + 1` done (ii) The shell script using the for loop is: #!/bin/sh # Displaying current processes in the system every 30 seconds for i in 1 2 3 4 5 do ps sleep 30 done
Solutions to Chapter Thirteen Questions 1. Write a shell script modch.sh that uses chmod to change the access permissions on a file so that only t he owner may
read, write, or execute it. Be sure to label the output to show what was done to the file. Ans.
#!/bin/sh #Label the output of chmod echo "Enter the name of the fil e, whose permissions you want to change" read filename echo "Before changing the file permissions, File permissions for the owner of the $1 file are: `ls -l $filename|tr -s " "|cut -c 2,3,4`" echo "Before changing the file permissions, File permissions for the group owner of the $1 file are: `ls -l $filename|tr -s " "| cut -c 5,6,7`" echo "Before changing the file permissions, File permissions for the other users of the $1 file are: `ls -l $filename|tr -s " "| cut -c 8,9,10`" echo "--------Changing the fi le permissions--------" chmod u+rwx,go-rwx $filename echo "After changing the file permissions, File permissions for the owner of the $1 file are: `ls -l $filename|tr -s " "|cut -c 2,3,4`" echo "After changing the file permissions, File permissions for the group o wner of the $1 file are: `ls -l $filename|tr -s " "| cut -c 5,6,7`" echo "After changing the file permissions, File permissions for the other users of the $1 file are: `ls -l $filename|tr -s " "|cut -c 8,9,10`"
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2. Modify the del script so t hat it detects whether the user has specified a directory to be deleted, in which case the script
should call the rmdir command. (Hint: use the test with the -d option to test for a directory.) 11. Rewrite Rewrite tickle tickle to use an an if/then/elif if/then/elif/...../fi /...../fi struct structure. ure. 12. Rewrite Rewrite echo.sh echo.sh to use use an until loop. Ans.
The del script: #!/bin/sh #Delete a file or directory interactively filename=$1 if test -f $filename then echo "Do you want to delete \"$filename\"?" read choice if test $choice == y then rm $filename echo "\"$filename\" deleted." else echo "\"$filename\" not deleted." fi elif test -d $filename then echo "Do you want to delete \"$filename\"?" read choice1 if test $choice1 == y then echo "Do you want to delete the subdirectories also?" read ans if test "$ans" == "y" then rm -r $filename else echo "\"$filename\" not deleted." fi fi else echo "\"$filename\" does not exist." fi
1. The tickle script: #!/bin/sh # A daily reminder service set `date`
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echo "Remember for today" if [ $1 == "Mon" ] then echo "Plan the week."; elif [ $1 == "Tue" ] then echo "Take clothes to the cleaners."; elif [ $1 == "Wed" ] then echo " Attend group meeting."; elif [ $1 == "Thu" ] then echo "Make plans for the weekend."; echo "Pick up clothes at the cleaners."; elif [ $1 == "Fri" ] then echo "Answer e-mail."; elif [ $1 == "Sat" ] then echo "You should not be here working."; echo "Finish your work and log off."; elif [ $1 == "Sun" ] then echo "Call Grandma and Grandpa."; else echo "Invalid day"; fi
2. The echo.sh script: #!/ bin/sh # Echo a line 'n' times count=$1 shift message=$* until test $count -eq 0 do echo $message count=`expr $count - 1` done
3. The lshead.sh script: #Labeling the output of ls -l command echo
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echo "Displaying the output of ls-l" echo ls -l | grep [-rwx] > try echo "FAP cat try | more
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Links Owner
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Filename"
