KU ASSIGNMENT 4TH SEM: TB – 43 – UNIX & SHELL PROGRAMMING
PART – A
1. What are the different standard given by POSIX ? What is POSIX ?
Ans. :- The different standard given by POSIX are:-
* POSIX.1
* POSIX.1B
* POSIX.1C
* POSIX.2
* POSIX:2001
* POSIX:2004
* POSIX:2008
POSIX is the Portable Operating System Interface, the open operating interface standard accepted world-wide. It is produced by IEEE and recognized by ISO and ANSI.
2. On which variable terminal setting is done ? Name any three terminal setting
keys.
Ans.:- Using STTY
Three terminal setting key
quit, kill, erase, …
The environment variable TERM is used to identify the type of terminal (or terminal emulator) to the curses library and programs that use the curses library to display text. It is also associated with the TERMINFO and (in archaic systems) TERMCAP environment variables
3. Explain key features of UNIX.
Ans. :- The UNIX system is supported by the file and the process. Directories and devices are treated as files and there are many text manipulation tools to edit these files. When a file is executed as a program, it is called a process. There are tools to control processes like sending a processes into background or even terminating it.
Unix is a multitasking operating system, which allows the computer to run several programs at the same time. By going quickly from one task to another and performing a little bit of each task every time, the operating system gives an impression of doing many things at the same time. Unix uses this technique of time-sharing. Unix is also able to interact with more than one user at a time. This feature of Unix makes it a multitasking system.
4. What is script command, with command explain how to create script file of a
session?
Ans.-
5. What happens if a directory permission charged?
Ans.- Every time a file or a directory is created, default permissions are established
for it. These default permissions are initially assigned either by the operating
system or the program being run. Setting default permissions saves us the
trouble of specifying permission codes explicitly every time a file or directory is
created. The operating system assigns the default permission values of 777 for
executable files and 666
for all other files.
To put further restrictions on the permissions assigned by a program when it
creates a file or directory, a user mask is specified with the umask command.
The user mask is a numeric value that determines the access permissions when a
file or directory is created. Consequently, when a file or directory is created, its
permissions are set to the permissions specified by the creating program minus
the permission values denied by the umask value.
Example
The command umask without arguments gives the octal value of the user mask.
$ umask
022
6. How do you yank and paste lines?
Ans. :- The command ‘Y’ or ‘yy’ copies (yanks) one or more lines. To copy one line, two lines, 10 lines, and all lines to the end of the file, respectively:
Y 2Y 10Y yG
To paste the text contained in the buffer above (uppercase P) or below the current cursor position (lowercase p), respectively:
P p
It is also possible to yank text within a line. The following commands yank text from the current cursor position to the end of the word and the end of the line, respectively:
yw y$
The same commands paste the text within a line. Lower case p pastes after the cursor position and upper case P pastes before.
Paste will also work with deleted text, either lines or parts of lines. Be careful not to execute any other commands prior to pasting as this will empty the buffer.
7. List out the different attributes of a file.
Ans.:- Listing File Attribute:-
-rw-r—– 1 sibnas sibgrp 4562 sep 22 10:30
-rw-r—– 1 sibnas sibgrp 8976 sep 22 10:30
-rw-r—– 1 sibnas sibgrp 10234 sep 22 10:30
-rw-r—– 1 sibnas sibgrp 4352 sep 22 9:30
-rw-r–r–r- 1 sibnas sibgrp 87632 aug 2 11:30
-rw-r–r–r- 1 sibnas sibgrp 6528 june 20 10:30
-rw-r–r–r- 1 sibnas sibgrp 9234 may 22 10:00
File type link User id group id file size date &
Count in bytes of modi.
8. 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.
c. ZZ
9. Write general syntax of CASE statements.
Ans. :- The case statement compares word with pattern; if they match ,the shell runs the command on the first line. Otherwise the shell checks the remaining patterns ,one by one ,until it finds one that matches the word; it then runs the command on that online.
Syntax for case statement:-
#!/bin/sh
Set „date?
Case $1 in
Fri) echo “thank goodness it?s Friday!”;;
Sat | Sun) echo “you should not work on week-ends”;
Echo “log off and go home!”;;
*) echo “it is not yet the weekend.”;
Echo “get to work! “;;
esac
10. What is a process ? Name two important attributes of a process.
Ans :- Process is born when a program starts execution and exists as long as
the program is running. After execution the process is usually the name of the
program being executed.
The two important attribute of a process are:-
1) The process-id(PID).Each process is identified by a unique number called
the process-id which is allotted by the kernel when the process is born.
2) The parent PID(PPID) the PID of the parent is also a process attribute.
When many processes have the same PPID it is easier to kill the parent
process rather than the children separately.
PART – B
1. a) Explain layered architecture of unix operating system. With a suitable
command explain the interaction between Shell and Kernel.
Ans.:-Unix, like other operating systems, is a layer between the hardware and the applications that run on the computer. it has functions that manage the hardware functions that manage executing applications. So what?s h difference between UNIX and any other operating system? Basically two things: internal implementation and the interface that is seen and used by users.
The part of UNIX that manages the hardware and the executing processes is called the kernel. The kernel is collection of programs written in c which directly communicate with the hardware . Application programs communicate with the hardware by using the services of Kernel. Along with the memory management, the kernel also schedules processes and decides their priorities.
In the Unix system , each hardware device is viewed as a file and is called a device file .this allows the same simple method of reading and writing files to be used to access each hardware device.
The user commands are translated in to action by the shell which acts as interpreter. The shell forms the outer part of the operating systems and forms the interface between the user and kernel. for each user logged in, there is shell in action. When a command is
given by the user, it is examined by the shell and communicated to the kernel for execution.
Application portability is the ability of a single application to be executed on various types of computer hardware without being modified. This can be achieved if the application uses the UNIX interface to manage its hardware needs.
b) Explain uname command with different options.
Ans.:- uname – displays the name of the operating system
Syntax
uname [options]
Examples:
Displays all the information
$uname –a
SCO_SV sco5 3.2 5.0.5 i386
Displays the machine?s node name in the communication network.
$uname-n
Sco-5
Displays the operating system release.
$uname-r
3.2
Displays the name of the operating system
$uname –s
SCO_SV
Displays the operating system version
$uname –v
5.0.5
Displays the information about system name, node name, operating system
release number, kernel ID, processor type, serial number, number of users
license, OEM number, origin number and number of CPUs.
2. a) Explain the advantages of ispell, list out the basic commands used in ispell.
Ans.:-
b) Explain unix file system and give the difference between relative and absolute
path name.
Ans.:-Unix file system can be defined as belonging to one of four possible types:-
Ordinary files: ordinary files can contain text, data, or program information. An ordinary file cannot contain another file, or directory. An ordinary file can be a text file or binary file. Most of the UNIX command are binary files.
Directory files :- Directories are containers that can hold files, and other directories. A directory is actually implemented as a file that has one line for each item contained within the directory. Each line in a directory file contains only the name of the item, and a numerical reference to the location of the item.
Special files :- Special files represent i/o devices like, a tty, a disk drive, or a printer. Because UNIX treats such devices as files. Some of the commands used to access ordinary files will also work with devices files. This allows more efficient use of software.
Links:- A link is a pointer to another file. Since a directory is alist of the names and i-numbers of files, directory entry can be a hard link. In which the i-number points directly to another file. A hard link to a file cannot be distinguished from the file itself.
Difference between ABSOULATE AND RELATIVE PATHNAMES
ABSOULATE PATHNAMES
RELATIVE PATHNAMES
An Absoulate pathname specifies the location of a file .
Relative pathname specifies a file in relation to the current directory.
An Absoulate pathname starts at the / root directory.
A Relative pathname starts from the current directory.
An Absoulate pathname uses a slash (/) between each directory name in the path to indicate different directories.
In a Relative pathname, a single dot (.) represents the current working directory and two dots (..) represent the parent of the current working directory.
3. a) Explain how to split file into multiple files. Give suitable example.
Ans. :- we used “split” command to split file into multiple files.
split – split large files into “smaller files”
syntax –
split[options] filename prefix
where file name is the name of the large file to be split ,prefix is the name to be given the small output files and options can either be excluded or can be one of the or can be one of the following:-
-l = linenumber
-b = bytes
If –l option is used, linenumber will be the number of the lines to be put in each of the smaller files (the default is 1000). If the –b option is used ,bytes will be the number of bytes to be put in each of the smaller files.
The split command will give each output file created the name prefix with an extension attached to the end to indicate its order
EXAMPLE :
Assuming that file.txt is 3000 lines long , it will output three files, xaa, xab, and xac, and each one will be 1000 lines long.
$ splitfile.txt
This will output six soo-line files: fileaa, fileab, fileac,filead, fileae, and fileaf.
$split-1500 file.txt file
Assuming that file.txt has 200 kb ,this will output five 40 kb files: fileaa, fileab, fileac ,filead, fileae, and fileaf.
$ split –b 40k .txt file
b) Give the difference between Hard Link and Symbolic Link.
Ans: – Soft Link:
– Soft links are links to a file but not the inode.
– Created using
ln -s file1 file2
=> ls -il
131135 lrwxrwxrwx 1 user user 5 Jul 10 09:04 file2 -> file1
131137 -rw-r–r– 1 user user 35 Jul 10 09:03 file1
– The inode for file1 is 131137 and inode for file2 is 131135.
– If you see the permission bits, there is ‘l’ in the front for a soft link.
– If file1 is deleted, the link still exists. But if you try to view file2, its empty. This means that once the main file is deleted the data is gone.
Hard Link:
– Hard links are links to inode
– Created using
ln file1 file2
=> ls -il
131136 -rw-r–r– 2 user, user 48 Jul 10 09:27 file1
131136 -rw-r–r– 2 user, user 48 Jul 10 09:27 file2
– The inode for file1 and file2 is the same (131136).
– If you see the output above for “ls -i”, file2 does not show that it is linked to file1. In reality it is not linked to file1 but it is linked to the inode.
– If you see that there is number ’2? before the username ‘user’. This shows the number of hard links to the inode.
– If file1 is deleted, the data is not deleted. If you view file2 the data is still there. Deleting file1 only deletes a link. The data is gone once the last hard link is deleted.
4. a) What is a process? Explain the mechanism of creation in unix.
Ans :- A process is a collection of interrelated work tasks initiated in response to an event that achieves a specific result for the customer of the process. Adding more specific detail to that general definition:
* that achieves a specific result:
* must deliver a specific result
this result must be individually identifiable and countable
a good process name clearly indicates the result or end state of the process
* for the customer of the process:
* a customer receives the result or is the beneficiary of it
the customer can be a person or an organization
customer can be identified and can pass judgment on the result and process
customer point of view helps identify and name the process accurately
* initiated in response to a specific event:
* the process must be initiated in response to a specific event
multiple events can initiate a process
having an event AND a result allows the tracing of the sequence of tasks that turns the event into the result
* work tasks:
* a collection of actions, activities, steps or tasks make up a business process
a step in the initial workflow will probably be divided into more detailed steps later
* a collection of interrelated:
* the process steps must relate to each other
interrelationship is through sequence and flow…the completion of one step leads to (flows into) the initiation of the next step
also interrelated by dealing with the same work item
steps related by being traceable back to the same initiation event
b) List out the navigation keys for the cursor movement.
Ans. :- in the command mode ,navigation keys for the movement of the cursor by characters, words and lines are as follows:
Keys
Movement of cursor
H
Cursor moves left
J
Cursor moves down
K
Cursor moves up
L
Cursor moves right
W
Word forward
B
Word backward
E
End of word
^
First character
$
End of line
0
Beginning of line
The screen display can be controlled by scrolling the display forward and backward using the following keys:-
Keys
Screen display
[ctrl-f]
Scroll display forward
[ctrl-h]
scroll display backward
[ctrl-d]
Scroll half-screen forward
[ctrl-u]
Scroll half-screen backward
5. a) Explain grep command with at least 5 examples with different options.
Ans.- 1) A simple Linux grep example – searching for a text string in one file
This first grep command example searches for all occurrences of the text string ‘fred’ within the “/etc/passwd” file. It will find and print (on the screen) all of the lines in this file that contain the text string fred, including lines that contain usernames like “fred” – and also “alfred”.
grep ‘fred’ /etc/passwd
In a simple grep example like this, the quotes around the string fred aren’t necessary, but they are needed if you’re searching for a string that contains spaces, and may be needed when you get into using regular expressions (search patterns).
2) Linux grep command – searching for a string in multiple files
Our next grep command example searches for all occurrences of the text string joe within all files of the current directory:
grep ‘joe’ *
The ‘*’ wildcard matches all files in the current directory, and the grep output from this command will show both (a) the matching filename and (b) all lines in all files that contain the string ‘joe’.
As another example, you can also use grep to search all files in the current directory that end in the file extension “.txt”, as shown here:
grep ‘joe’ *.txt
3) Case-insensitive file searching with the Unix grep command
To perform a case-insensitive search with the grep command, just add the -i option, like this:
grep -i score gettysburg-address.txt
This grep search example matches the string “score”, whether it is uppercase, lowercase, or any mix of the two.
4) Reversing the meaning of a grep search
You can reverse the meaning of a Linux grep search with the -v option. For instance, to show all the lines of my /etc/passwd file that don’t contain the string fred, I’d issue this grep command:
grep -v fred /etc/passwd
5) Using grep in a Unix/Linux command pipeline
The grep command is often used in a Unix/Linux pipeline. For instance, to show all the Apache httpd processes running on my Linux system, I can use the grep command in a pipeline with the ‘ps’ command:
ps auxwww | grep httpd
b) Explain Uniq command.
Ans.- The default output is to display lines that only appear once and one copy of lines that appear more than once. It is also useful to filter out multiple blank lines from unsorted output of other commands. For example, the dircmp command displays its output using pr; thus the output usually scrolls off your screen before you can read it. But if you pipe the output of the dircmp command through the uniq command, the blank lines are reduced and the output is more compact.
* -u Print only lines which are not repeated (unique) in the original file
* -d Don’t output lines that are not repeated in the input.
* -c Generate an output report in default style except that each line is preceded by a count of the number of times it occurred. If this option is specified, the -u and -d options are ignored if either or both are also present.
* -i Ignore case differences when comparing lines
* -f Ignore a number of fields in a line
* -s Skips a number of characters in a line
* -w Specifies the number of characters to compare in lines, after any characters and fields have been skipped
* –help Displays a help message
* –version Displays version number on stdout and exits.
6. a) Explain the mechanism of executing job periodically using cron.
Ans. A task can be automatically run in the background at regular intervals by a Unix utility called cron.
The cron daemon takes care of running these background jobs, which are called cron jobs.
crontab or the crontable is a file which contains the schedule of cron entries to be run and at specified times. cron checks the crontable at regular tables to see if there are any jobs scheduled. A user can execute crontab if the user?s name appears in the file /usr/lib/cron/cron.allow. If the cron.allow does not exist, the cron.deny file in /usr/lib/cron is checked. If the user?s name is not in this file the user is allowed to use crontab. If only cron.deny exists and is empty, all users can use crontab. If neither file exists, only the root user can use crontab. The allow and deny files contain one user name per line.
b) Write a shell script to add two numbers by using Expr utility.
Ans.:- To use it in a shell script, you simply surround the expression with backquotes. For
example, let?s write a simple script called add that adds two numbers typed as arguments:
# /bin/sh
# Shell Script to Add two numbers
sum=„expr $1 + $2„
echo $sum
Here we defined a variable sum to hold the result of the operation. (Note the spaces around the plus
sign, but not around the equals sign). To run this script, we might type the following line: (assume the script
add is executable)
$ add 4 3
The first argument (4) is stored in $1, and the second (3) is stored in $2. The expr utility then adds
these quantities and stores the result in sum. Finally, the contents of sum are echoed on the screen:
7
$
The expr command only works on integers (i.e., whole numbers). It can perform addition (+), subtraction
(-), multiplication (*), integer division (/), and integer remainder (%).
7. a) What are positional parameters? Explain the command used to set the
positional parameters.
Ans. – These are used by the shell to store the values of command-line
arguments.
The command which used to set the positional parameter
#!/bin/sh
# Demonstrate the set command
set „date„
echo “Time: $4 $5”
echo “Day: $1”
echo “Date: $3 $2 $6”
Assuming that setdate has been made executable with the chmod command, we can run the script by
typing the command
$ setdate
The output will look something like this:
Time:10:56:08 EST
Day: Fri
Date: 20 Aug 2004
What happened? Consider the command line
set „date„
The backquotes run the date command, which produces output something like this:
Fri Aug 20 10:56:08 EST 2004
This does not appear on the screen. Instead, the set command catches the output and stores it in the
positional parameters $1 through $6:
$1 contains Fri
$2 Contains Aug
$3 contains 20
$4 contains 10:56:08
$5 contains EST
$6 contains 2004
b) Explain Head Command with example.
Ans :- The head command, as the name implies, displays the top of the file. When used without an option, it
displays the first ten lines of the file.
You can use the –n option to display the first „n? number of lines.
$ head emp.lst Shows first ten lines of the emp.lst file
The head command, as the name implies, displays the top of the file. When used without an option, it
displays the first ten lines of the file.
You can use the –n option to display the first „n? number of lines.
$ head emp.lst Shows first ten lines of the emp.lst file
1001|T.N.Raju |Professor |Information Science|14/06/61|30000
1004|D.S.Raghu |Lecturer |Information Science|05/12/75|17000
1005|S.K.Anantha |Asst.Prof. |Information Science|20/07/63|24000
1009|M.P.Rajendra |Sr.Lecturer |Computer Science |13/03/66|20000
1002|Mallu |Lecturer |Information Science|20/07/74|15000
8. a) What are positional parameters? Explain the command used to set the
positional parameters.
Positional paremeters:-These are used by the shell to store the values of command-line
arguments.
The command which are used to set the positional parameter
#!/bin/sh
# Demonstrate the set command
set „date„
echo “Time: $4 $5”
echo “Day: $1”
echo “Date: $3 $2 $6”
Assuming that setdate has been made executable with the chmod command, we can run the script by
typing the command
$ setdate
The output will look something like this:
Time:10:56:08 EST
Day: Fri
Date: 20 Aug 2004
What happened? Consider
set „date„
The backquotes run the date command, which produces output something like this:
Fri Aug 20 10:56:08 EST 2004
This does not appear on the screen. Instead, the set command catches the output and stores it in the
positional parameters $1 through $6:
$1 contains Fri
$2 Contains Aug
$3 contains 20
$4 contains 10:56:08
$5 contains EST
b) Explain Head Command with example.
“head command ” displays the top of the file.
Example:-
$ head emp.1st
It displays the first ten lines of the file.
We can use –n option with the head command to display the first „n? number of lines.
$ head – n 3 emp.1st
This displays the first 3 lines of the file.
8. Explain the options and associated actions for ls command.
Ans :- The Is command shows the contents of a directory , and a view of basic information (like size ,ownership, and access permission) about files and directories.
The options and associated actions for Is command are:
OPTION
ACTION
-1
One file name in each line
-a
All files including those beginning with a dot(.), current directory (.) and directory above (..)
-A
All files including those beginning with a dot(.).does not list current directory(.) and directory above.
-d
If an argument is a directory ,lists only its name (not its contents)
-F
Marks directories with a /,executables with a * and symbolic links with a @
-I
Shows the inode number
-l
Lists in long format , giving mode, number of links, owner, group, size in bytes, the time that each file was last modified.
-p
Puts a slash (/) after each directory.
-r
Sorts the filenames in the reverse order
-R
Recursive list
-t
Sorts by time modified (latest first)
-u
Sorts by last access time.
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