unix-lab

UNIX Tutorial One

50

Introduction

The first script that we will use will be a simple script that will output the text Hello Unix. I would suggest using vi to create and edit the file. To create and edit the file, run the following command:

vi hello.sh

If you dont know how to use vi, I would suggest that you read a quick tutorial by searching for vi tutorial with the search bar above. To enter input mode in vi, press i. Now, for the code in this first script, enter the following code in the file:

#!/bin/sh

# This is my first script.

echo "Hello Unix"

Now save the file and close it by hitting Escape followed by :wq and Return. The first line of the file tells unix which shell to use to execute the file. /bin/sh is the default location for the bourne shell. In Linux this will normally point to the bourne again shell, which is a remake of the original unix shell and works pretty much the same. The second line of the file is just a simple comment. Comments are ignored by the shell interpreter but are very useful when developing large and complex scripts. Everyone forgets what their original logic or intention was when coding a script and its much easier to read a comment than it is to try to understand large and complex sections of code. Before we can run this script, we must first make it executable. To do this we will use the unix chmod command:

chmod u+x hello.sh

Now our script is executable. This command basically tells unix to set the x (executable) flag for the user level access of the file. Now we are able to run the file. If you dont have . in your unix PATH environment variable, then you will need to proceed the name of the script with ./ to execute it. It is generally considered to be a security risk to put . in your PATH evironment variable, so we will assume that you dont have it. Now you can execute your script by using the following command:

./hello.sh

You will see the text Hello Unix output to the console, congratulations, you have created your first unix script!

Variables

Variables are an important part of any program or script. A variable is a simple way to refer to a chunk of data in memory that can be modified. A variable in a unix script can be assigned any type of value, such as a text string or a number. In unix to create a variable, we simply put in our script:

VARIABLE_NAME=value

Note that we do not have to put the variable name in uppercase, but it is the standard way of naming variables in unix. The text VARIABLE_NAME can be anything you want, as long as it only contains numbers, letters and/or an underscore _. A variable name also cannot start with a number. After the equal sign you put the value, there must be no space between the variable name and the equal sign. To use the variable, we simply put a dollar sign $ before the name of the variable in our script code. Lets revise our original script to use the two words in two variables as such:

#!/bin/sh

# This is my second script.

VAR_1=Hello

VAR_2=Unix

echo "$VAR_1 $VAR_2"

This gives the same output as the original script but uses two variables. This is not a very exciting use of variable I will admit, lets try something more interesting. Lets write a program that will open a file and read the head and tail of it. This can be useful if you want to see the first items in your log and the last items in your log but you dont want to see the whole log file, which could be very large. To write this program, we will make use of the unix commands head and tail. Our script will use a predefined varible called $1. This variable will display the first item in the list of command line arguments to your script. You can also access any other command line argument from $1 to $9. You can also use the variable $@ to access all of the command line arguments in a single variable.

#!/bin/sh

# This program will print the head and tail of a file

# passed in on the command line.

echo "Printing head of $1..."

head $1

echo "" #this prints an extra return...

echo "Printing tail of $1..."

tail $1

Give this program a name of ht.sh (for Head Tail shell script), be sure to give it execute permission and then run it with the following command:

./ht.sh WEB_LOG

The parameter WEB_LOG must point to an actual text file on your system, it will open the file and print the head and tail. Now lets assume that we want the user to be able to input the file name after the script has been run. We can read input from the console by using the unix read command. Lets modify the program and try it again:

#!/bin/sh

# This program will read the filename from user input.

echo "Enter the file: "

read FILENAME

echo "Printing head of $FILENAME..."

head $FILENAME


echo "Printing tail of $FILENAME..."

tail $FILENAME

This way of printing a variable does have limitations, for instance you cannot print text without a space after the variable name. Suppose that we want to create a script that will read the head and tail of the file as before, but we know that the user will always be using files that end with _LOG. If we tried to open the file $FILENAME_LOG, then it would look for a variable with that specific name and not a file named $FILENAME + _LOG.

We can fix this by using another way of displaying and using a variable. We use the format ${VARIABLE_NAME}. Lets modify our program again to automatically append _LOG to the end of the filename for our users:

#!/bin/sh

# This program will read the filename from user input.

echo "Enter the file: "

read FILENAME

echo "Printing head of ${FILENAME}_LOG..."

head ${FILENAME}_LOG


echo "Printing tail of ${FILENAME}_LOG..."

tail ${FILENAME}_LOG

Now if you run the script with the command ./ht.sh WEB it will open the file WEB_LOG for the user.

Unix Lab(doc)INDEXS.NoContentsPage No.

1Lab Objective2

2Introduction About Lab3

3Guidelines to Students 5

4List of Syllabus Programs7

5Description about UNIX commands10

6Discription about shells20

6Solutions for Programs 22

7Viva Questions and Answers 35

8References55

1. Demonstrate how to use the following Bourne Shell commands: cat, grep, ls, more, ps, chmod, finger, ftp, etc.

2. Use the following Bourne Shell constructs: test, if then, if then else, if then elif, for, while, until, and case.

3. Learn tracing mechanisms (for debugging), user variables, BourneShell variables, read-only variables, positional parameters, reading input to a BourneShell script, command substitution, comments, and exporting variables. In addition, test on numeric values, test on file type, and test on character strings are covered.

4. Copy, move, and delete files and directories

5. Write moderately complex Shell scripts.

6. Make a Shell script executable.

7. Create a ".profile" script to customize the user environment.

8. Use advanced features of File Transfer Protocol (FTP)

9. Compile source code into object and executable modules.

10. Execute programs written in c under UNIX environment

How to Run Shell Scripts

There are two ways you can execute your shell scripts. Once you have created a script file:

Method 1

Pass the file as an argument to the shell that you want to interpret your script.

Step 1 : create the script using vi, ex or ed

For example, the script file show has the following lines

echo Here is the date and time

date

Step 2 : To run the script, pass the filename as an argument to the sh (shell )

$ sh show

Here is the date and time

Sat jun 03 13:40:15 PST 2006

Method 2:

Make your script executable using the chmod command.

When we create a file, by default it is created with read and write permission turned on and execute permission turned off. A file can be made executable using chmod.

Step 1 : create the script using vi, ex or ed

For example, the script file show has the following lines

echo Here is the date and time

date

Step 2 : Make the file executable

$ chmod u+x script_file

$ chmod u+x show

Step 3 : To run the script, just type the filename

$ show

Here is the date and time

Sat jun 03 13:40:15 PST 2006

How to run C programs

Step 1 : Use an editor, such as vi, ex, or ed to write the program. The name of the file containing the program should end in .c.

For example, the file show.c contains the following lines :

main()

{

printf( welcome to GNEC );

}

Step 2 : Submit the file to CC ( the C Compiler )

$ cc show.c

If the program is okay, the compiled version is placed in a file called a.out

Step 3 : To run the program, type a.out

$ a.out

Welcome to GNEC

Basic Unix commandsCommandCAT

Syntaxcat [argument] [specific file]

Descriptioncat" is short for concatenate. This command is used to create, view and concatenate files.

Examplescat /etc/passwd This command displays the "/etc/passwd" file on your screen.

cat /etc/profile This command displays the "/etc/profile" file on your screen. Notice that some of the contents of this file may scroll off of your screen.

cat file1 file2 file3 > file4 This command combines the contents of the first three files into the fourth file.

Command pwd

Syntax pwd

Description "pwd" stands for print working directory. It displays your current position in the UNIX filesystem.

Examples pwd There are no options (or arguments) with the "pwd" command. It is simply used to report your current working directory.

Command ls

Syntax ls [options] [names]

Description "ls" stands for list. It is used to list information about files and directories.

Examples ls

This is the basic "ls" command, with no options. It provides a very basic listing of the files in your current working directory. Filenames beginning with a decimal are considered hidden files, and they are not shown.

ls -a

The -a option tells the ls command to report information about all files, including hidden files.

ls -l

The -l option tells the "ls" command to provide a long listing of information about the files and directories it reports. The long listing will provide important information about file permissions, user and group ownership, file size, and creation date.

ls -al

This command provides a long listing of information about all files in the current directory. It combines the functionality of the -a and -l options. This is probably the most used version of the ls command.

ls -al /usr

This command lists long information about all files in the "/usr" directory.

ls -alR /usr | more

This command lists long information about all files in the "/usr" directory, and all sub-directories of /usr. The -R option tells the ls command to provide a recursive listing of all files and sub-directories.

ls -ld /usr

Rather than list the files contained in the /usr directory, this command lists information about the /usr directory itself (without generating a listing of the contents of /usr). This is very useful when you want to check the permissions of the directory, and not the files the directory contains.

Command mv

Syntax mv [options] sources target

Options-b backup files that are about to be overwritten or removed

-i interactive mode; if dest exists, you'll be asked whether to overwrite the file

Description The "mv" command is used to move and rename files.

Examples mv Chapter1 Chapter1.bad This command renames the file "Chapter1" to the new name "Chapter1.bad".

mv Chapter1 garbage This command renames the file "Chapter1" to the new name "garbage". (Notice that if "garbage" is a directory, "Chapter1" would be moved into that directory).

mv Chapter1 /tmp This command moves the file "Chapter1" into the directory named "/tmp".

mv tmp tmp.oldAssuming in this case that tmp is a directory, this example renames the directory tmp to the new name tmp.old.

Command rm

Syntaxrm [options] files

Options-d, --directory

unlink FILE, even if it is a non-empty directory (super-user only)

-f, --force

ignore nonexistent files, never prompt

-i, --interactive

prompt before any removal

-r, -R, --recursive

remove the contents of directories recursively

-v, --verbose

explain what is being done

Description The "rm" command is used to remove files and directories. (Warning - be very careful when removing files and directories!)

Examples rm Chapter1.bad

This command deletes the file named "Chapter1.bad" (assuming you have permission to delete this file).

rm Chapter1 Chapter2 Chapter3 This command deletes the files named "Chapter1", "Chapter2", and "Chapter3".

rm -i Chapter1 Chapter2 Chapter3 This command prompts you before deleting any of the three files specified. The -i option stands for inquire. You must answer y (for yes) for each file you really want to delete. This can be a safer way to delete files.

rm *.htmlThis command deletes all files in the current directory whose filename ends with the characters ".html".

rm index*This command deletes all files in the current directory whose filename begins with the characters "index".

rm -r new-novel This command deletes the directory named "new-novel". This directory, and all of its' contents, are erased from the disk, including any sub-directories and files.

Command cp

Syntaxcp [options] file1 file2 cp [options] files directory

Options-b backup files that are about to be overwritten or removed

-i interactive mode; if dest exists, you'll be asked whether to overwrite the file

-p preserves the original file's ownership, group, permissions, and timestamp

Description The "cp" command is used to copy files and directories.

Note that when using the cp command, you must always specify both the source and destination of the file(s) to be copied.

Examples cp .profile .profile.bak This command copies your ".profile" to a file named ".profile.bak".

cp /usr/fred/Chapter1 . This command copies the file named "Chapter1" in the "/usr/fred" directory to the current directory. This example assumes that you have write permission in the current directory.

cp /usr/fred/Chapter1 /usr/mary This command copies the "Chapter1" file in "/usr/fred" to the directory named "/usr/mary". This example assumes that you have write permission in the "/usr/mary" directory.

Command grep

Syntax grep [options] regular expression [files]

Options-i case-insensitive search

-n show the line# along with the matched line

-v invert match, e.g. find all lines that do NOT match

-w match entire words, rather than substrings

Description Think of the "grep" command as a "search" command (most people wish it was named "search"). It is used to search for text strings within one or more files.

Examples grep 'fred' /etc/passwd This command 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 This command searches for all occurrences of the text string 'fred' within the "/etc/passwd" file, but also requires that the "f" in the name "fred" be in the first column of each record (that's what the caret character tells grep). Using this more-advanced search, a user named "alfred" would not be matched, because the letter "a" will be in the first column.

grep 'joe' * This command searches for all occurrences of the text string 'joe' within all files of the current directory.

Command mkdir

Syntax mkdir [options] directory name

Description The "mkdir" command is used to create new directories (sub-directories).

Examples mkdir tmp This command creates a new directory named "tmp" in your current directory. (This example assumes that you have the proper permissions to create a new sub-directory in your current working directory.)

mkdir memos letters e-mailThis command creates three new sub-directories (memos, letters, and e-mail) in the current directory.

mkdir /usr/fred/tmp This command creates a new directory named "tmp" in the directory "/usr/fred". "tmp" is now a sub-directory of "/usr/fred". (This example assumes that you have the proper permissions to create a new directory in /usr/fred.)

mkdir -p /home/joe/customer/acme This command creates a new directory named /home/joe/customer/acme, and creates any intermediate directories that are needed. If only /home/joe existed to begin with, then the directory "customer" is created, and the directory "acme" is created inside of customer.

Command rmdir

Syntaxrmdir [options] directories

Description The "rm" command is used to remove files and directories. (Warning - be very careful when removing files and directories!)

Examples rm Chapter1.bad

This command deletes the file named "Chapter1.bad" (assuming you have permission to delete this file).

rm Chapter1 Chapter2 Chapter3 This command deletes the files named "Chapter1", "Chapter2", and "Chapter3".

rm -i Chapter1 Chapter2 Chapter3 This command prompts you before deleting any of the three files specified. The -i option stands for inquire. You must answer y (for yes) for each file you really want to delete. This can be a safer way to delete files.

rm *.htmlThis command deletes all files in the current directory whose filename ends with the characters ".html".

rm index*This command deletes all files in the current directory whose filename begins with the characters "index".

rm -r new-novel This command deletes the directory named "new-novel". This directory, and all of its' contents, are erased from the disk, including any sub-directories and files.

Command cd, chdir

Syntax cd [name of directory you want to move to]

Description "cd" stands for change directory. It is the primary command for moving around the filesystem.

Examples cd /usr This command moves you to the "/usr" directory. "/usr" becomes your current working directory.

cd /usr/fred Moves you to the "/usr/fred" directory.

cd /u*/f* Moves you to the "/usr/fred" directory - if this is the only directory matching this wildcard pattern.

cd Issuing the "cd" command without any arguments moves you to your home directory.

cd - Using the Korn shell, this command moves you back to your previous working directory. This is very useful when you're in the middle of a project, and keep moving back-and-forth between two directories.

Command kill

Syntaxkill [options] IDs

Description kill ends one or more process IDs. In order to do this you must own the process or be designated a privileged user. To find the process ID of a certain job use ps.

Examples

Command ps

Syntaxps [options]

Description The "ps" command (process statistics) lets you check the status of processes that are running on your Unix system.

Examples ps The ps command by itself shows minimal information about the processes you are running. Without any arguments, this command will not show information about other processes running on the system.

ps -fThe -f argument tells ps to supply full information about the processes it displays. In this example, ps displays full information about the processes you are running.

ps -eThe -e argument tells the ps command to show every process running on the system.

ps -efThe -e and -f arguments are normally combined like this to show full information about every process running on the system. This is probably the most often-used form of the ps command.

ps -ef | moreBecause the output normally scrolls off the screen, the output of the ps -ef command is often piped into the more command. The more command lets you view one screenful of information at a time.

ps -fu fredThis command shows full information about the processes currently being run by the user named fred (the -u option lets you specify a username).

Why Use Shells?Well, most likely because the are a simple way to string together a bunch of UNIX commands for execution at any time without the need for prior compilation. Also because its generally fast to get a script going. Not forgetting the ease with which other scripters can read the code and understand what is happening. Lastly, they are generally completely portable across the whole UNIX world, as long as they have been written to a common standard.

The Shell History:The basic shells come in three main language forms. These are (in order of creation) sh, csh and ksh. Be aware that there are several dialects of these script languages which tend to make them all slightly platform specific. Where these differences are known to cause difficulties I have made special notes within the text to highlight this fact. The different dialects are due, in the main, to the different UNIX flavours in use on some platforms. All script languages though have at their heart a common core which if used correctly will guarantee portability.

Bourne Shell:Historically the sh language was the first to be created and goes under the name of The Bourne Shell. It has a very compact syntax which makes it obtuse for novice users but very efficient when used by experts. It also contains some powerful constructs built in. On UNIX systems, most of the scripts used to start and configure the operating system are written in the Bourne shell. It has been around for so long that is it virtually bug free. I have adopted the Bourne shell syntax as the defacto standard within this book.

C Shell:Next up was The C Shell (csh), so called because of the similar syntactical structures to the C language. The UNIX man pages contain almost twice as much information for the C Shell as the pages for the Bourne shell, leading most users to believe that it is twice as good. This is a shame because there are several compromises within the C Shell which makes using the language for serious work difficult (check the list of bugs at the end of the man pages!). True, there are so many functions available within the C Shell that if one should fail another could be found. The point is do you really want to spend your time finding all the alternative ways of doing the same thing just to keep yourself out of trouble. The real reason why the C Shell is so popular is that it is usually selected as the default login shell for most users. The features that guarantee its continued use in this arena are aliases, and history lists. There are rumours however, that C Shell is destined to be phased out, with future UNIX releases only supporting sh and ksh. Differences between csh and sh syntax will be highlighted where appropriate.

Korne Shell:Lastly we come to The Korne Shell (ksh) made famous by IBM's AIX flavour of UNIX. The Korne shell can be thought of as a superset of the Bourne shell as it contains the whole of the Bourne shell world within its own syntax rules. The extensions over and above the Bourne shell exceed even the level of functionality available within the C Shell (but without any of the compromises!), making it the obvious language of choice for real scripters. However, because not all platforms are yet supporting the Korne shell it is not fully portable as a scripting language at the time of writing. This may change however by the time this book is published. Korne Shell does contain aliases and history lists aplenty but C Shell users are often put off by its dissimilar syntax. Persevere, it will pay off eventually. Any sh syntax element will work in the ksh without change.

SOLUTIONS:WEEK1

Session 1

1. Log in to the system

2. Use Vi editor to create a file called myfile.txt which contain some text.

3. Correct typing errors during creation

4. Save the file

5. Logout of the file

Sol:

$ login:

$ password: ******

$ vi

~ Unix is Case Sensitive

~ Never leave the Computer without logging out when you are working in a time sharing or network environments.

Type

: wq myfile

$

Session 2

1. Log into the system

2. Open the file created in session 1

3. Add some text

4. Change some text

5. delete some text

6. Save the changes

7. Logout of the system

Sol:

$ login:

$ password: ******

$ vi myfile

~ Unix is Case Sensitive

~ Never leave the Computer without logging out when you are working in a time sharing or network environments.

~ Shell Programming

: wq

WEEK2

Log into the system

Use the cat command to create a file containing the following data. Call it mutable use tabs to separate the fields

1425

ravi

15.65

4320

ramu

26.27

6830

sita

36.15

1450

raju

21.86

a. use the cat command to display the file, my table

b. use the vi command to correct any errors in the file, my table

c. use the sort command to sort the file my table according to the first field. Call the sorted file my table(same name)

d. print the file my table

e. use the cut & paste commands to swap fields 2 and 3 my table. Call it mytable(same name)

f. print the new file, my table

g. logout of the system

Sol:

$ login:

$ password:******

$ cat c1-14

1425

ravi

15.65

4320

ramu

26.27

6830

sita

36.15

1450

raju

21.86

$ cat myfile$who|more

$ sort +0 -1 mytable

WEEK3

a. log in the system

b. use the appropriate commands to determine ur login shell

c. use the /etc/passwd file to verify the result of step b.

d. use the who command redirect the result to a file called myfile1.Use the more command to see the contents of myfile1.

e. Use the date and who commands in sequence ?(in one line) such that the output of date will display on the screen and the output of who will be redirected to a file called my file2.Use the more command to check the contents of myfile2.

f. write a sed command that deletes the first character in each line in a file

g. write a sed command that deletes the character before the last character in each line in a file.

h. Write a sed command that swaps the files and second words in each line in a file

Sol:

$ login:

$ password:******

$ echo $SHELL

csh

$ who >| myfile1

$ more myfile1

$ date|who >myfile2

$ more myfile2

WEEK4

pipe ur /etc/passwd file to awk and print out the home directory of each user.

Develop an interactive grep script that asks for a word and a file name and then tells how many lines contain that word

Repeat

Part using awk

(d) Sol:

$ awk $2 ==Computers && $3 >10000 {print}Sales.dat

I/P:

1 Clothing 31411Computers9161

1Textbooks21312

2Clothing3252

2Computers1232

2Supplies2242

2Text books15462

O/P:

2Computers1232WEEK5

a) Write A shell script that takes a command line argument and reports on whether it is directry ,a file,or something else

b) Write a shell script that accepts one or more file name as a arguments and converts all of thenm to uppercase,provided they exits in the current directory

c) Write a shell script that determines the period for which a specified user is working on the system

(a) Sol:

echo "Enter a file name:"

read f

if [ -f $f ]

then

echo "File"

elif [ -d $f ]

then

echo "Directory"

else

echo "Not"

fi

Output:DirectoryWEEK6

(a) Write a shell script that accepts a file name starting and ending line numbers as arguments and displays all the lines between the given line numbers

(b) Write a shell script that deletes all lines containing a specified word I one or more files supplied as arguments to it.

(a) Sol:$ awk NR 4 {print $0} 5 lines.datI/P:line1line2

line3

line4

line5

O/P: line1

line5

(b) Sol:i=1

while [ $i -le $# ]

do

grep -v Unix $i > $i

done

WEEK7a) Write a shell script that computes the gross salary of a employee according to the following

1) if basic salary is 1500 then HRA 500 and DA =98% of the basic

The basic salary is entered interactively through the key board

(b)Write a shell script that accepts two integers as its arguments and computes the value of first number raised to the power of the second number

echo " Enter the Salary "

read sal

if [ $sal1500]hra=500da=expr $sal*98/100gsal=expr $sal+$hra+$dagross=`expr $sa + $da + $hra`fi

fi(b)a=$1

b=$2

c=pow($a,$b)

echo$c

WEEK 8

(a) Write an interactive file handling shell program. Let it offer the user the choice of copying ,removing ,renaming or linking files. Once the use has made a choice, have the program ask the user for necessary information, such as the file name ,new name and so on.

(b) Write a shell script that takes a login name as command line argument and reports when that person logs in

(c) Write a shell script which receives two files names as arguments. It should check whether the two file contents are same or not. If they are same then second file should be deleted.

PROGRAM

echo "Enter I File Name:"

read f1

echo "Enter II File Name:"

read f2

d=`cmp $f1 $f2`

d1=""

if [ $d -eq $d2 ]

then

echo "Two Files are similar and $f2 is deleted"

rm $f2

else

echo "Two Files differ each other"

fi

WEEK 9

(a) Write a shell script that displays a list of all files in the current directory to which the user has read write and execute permissions

(b) Develop an interactive script that asks for a word and file name and then tells how many times that word occurred in the file.(c) Write a shell script to perform the following string operations.

1) To extract a sub string from a given string

2) To find the length of a given string

(a) PROGRAM# File Name : list.sh

#!/bin/bash

read -p "Enter a directory name : " dn

if [ -d $dn ]; then

printf "\nFiles in the directory $dn are :\n"

for fn in `ls $dn`

do

if [ -d $dn/$fn ]; then

printf " Directory "

elif [ -f $dn/$fn ]

then

printf "$fn File "

fi

if [ -r $dn/$fn ]; then

printf " Read"

fi

if [ -w $dn/$fn ];then

printf " Write"

fi

if [ -x $dn/$fn ];then

printf " Execute"

fi

printf "\n"

done

else

printf "\n$dn not exists or not a directory"

fi

(b) PROGRAM # File Name : wcount.sh

#!/bin/bash

read -p "Enter a file name : " fn

if test -f $fn

then

echo "The contents of the file $fn is :"

cat $fn

echo "No. of Line : `wc -l $fn`"

echo "No. of Words : `wc -w $fn`"

echo "No. of Characters: `wc -c $fn`"

else

echo "$fn is not exists or not a file"

fi

(c) PROGRAMPrint Enter the String:\c

read strIn

strlen=${# strIn}

print the string length is : $strlen

$ strlen.scr

O/P:

Enter the String: Now is the time

The String length : 15

WEEK 10Write a C program that takes one or more file or directory names as command line input and reports the following information on the file.

1. file type

2. number of links

3. read, write and execute permissions

4. time of last access

(Note: use /fstat system calls)

PROGRAM#include

main()

{

FILE *stream;

int buffer_character;

stream=fopen(test,r);

if(stream==(FILE*)0)

{

fprintf(stderr,Error opening file(printed to standard error)\n);

fclose(stream);

exit(1);

}

}

if(fclose(stream))==EOF)

{

fprintf(stderr,Error closing stream.(printed to standard error)\n);

exit(1);

}

return();

}

WEEK 11

Write C program that simulate the following unix commands

(a) mv

(b) cp

/* File Name : bspace1.c */

#include

#include

#include

main(int argc,char *argv[])

{

FILE *fp;

char ch;

int sc=0;

fp=fopen(argv[1],"r");

if(fp==NULL)

printf("unable to open a file",argv[1]);

else

{

while(!feof(fp))

{

ch=fgetc(fp);

if(ch==' ')

sc++;

}

printf("no of spaces %d",sc);

printf("\n");

fclose(fp);

}

}

WEEK 12

Write a c program that simulates ls command

(Use system calls /directory API)

PROGRAM:#include

#include

#include

main(int argc,char *argv[])

{

int fd,i;

char ch[1];

if (argc0)

printf("%c",ch[0]);

close(fd);

}

Viva Questions & AnswersWhat is a Make file?Make file is a utility in Unix to help compile large programs. It helps by only compiling the portion of the program that has been changed

Could you tell something about the Unix System Kernel?The kernel is the heart of the UNIX operating system, its responsible for controlling the computers resources and scheduling user jobs so that each one gets its fair share of resources.

How can you tell what shell you are running on UNIX system?You can do the Echo $RANDOM. It will return a undefined variable if you are from the C-Shell, just a return prompt if you are from the Bourne shell, and a 5 digit random numbers if you are from the Korn shell. You could also do a ps -l and look for the shell with []

What do you mean by u-area (user area) or u-block?This contains the private data that is manipulated only by the Kernel. This is local to the Process, i.e. each process is allocated a u-area.

What scheme does the Kernel in Unix System V follow while choosing a swap device among the multiple swap devices?Kernel follows Round Robin scheme choosing a swap device among the multiple swap devices in Unix System V.

List the system calls used for process management:System calls Descriptionfork() To create a new processexec() To execute a new program in a processwait()[]

How do you change File Access Permissions?Every file has following attributes:owners user ID ( 16 bit integer )owners group ID ( 16 bit integer )File access mode wordr w x -r w x- r w x(user permission-group permission-others permission)r-read, w-write, x-executeTo change the access mode, we use chmod(filename,mode).Example:To change mode of myfile to rw-rw-r (ie. read, write permission for user - []

Explain the layered aspect of a UNIX system. What are the layers? What does it mean to say they are layers?A UNIX system has essentially three main layers:. The hardware. The operating system kernel. The user-level programsThe kernel hides the systems hardware underneath an abstract, high-level programming interface. It is responsible for implementing many of the facilities that users and user-level programs take for granted.The kernel assembles all of the following UNIX concepts from lower-level []

What is the use of grep command?grep is a pattern search command. It searches for the pattern, specified in the command line with appropriate option, in a file(s).Syntax : grep Example : grep 99mx mcafile

What difference between cmp and diff commands?cmp - Compares two files byte by byte and displays the first mismatchdiff - tells the changes to be made to make the files identical

What is the significance of the tee command?It reads the standard input and sends it to the standard output while redirecting a copy of what it has read to the file specified by the user.

Is du a command? If so, what is its use?Yes, it stands for disk usage. With the help of this command you can find the disk capacity and free space of the disk.

How to terminate a process which is running and the specialty on command kill 0?With the help of kill command we can terminate the process.Syntax: kill pid Kill 0 - kills all processes in your system except the login shell.

Explain kill() and its possible return values.There are four possible results from this call:kill() returns 0. This implies that a process exists with the given PID, and the system would allow you to send signals to it. It is system-dependent whether the process could be a zombie.kill() returns -1, errno == ESRCH either no process exists with the given PID, or []

What does the command $who | sort logfile > newfile do?The input from a pipe can be combined with the input from a file . The trick is to use the special symbol - (a hyphen) for those commands that recognize the hyphen as std input.In the above command the output from who becomes the std input to sort , meanwhile sort opens the file []

What are shell variables?Shell variables are special variables, a name-value pair created and maintained by the shell.Example: PATH, HOME, MAIL and TERM

How many prompts are available in a UNIX system?Two prompts, PS1 (Primary Prompt), PS2 (Secondary Prompt).

Is it possible to create new a file system in UNIX?Use su command. The system asks for password and when valid entry is made the user gains super user (admin) privileges.

How the Kernel handles the copy on write bit of a page, when the bit is set?In situations like, where the copy on write bit of a page is set and that page is shared by more than one process, the Kernel allocates new page and copies the content to the new page and the other processes retain their references to the old page. After copying the Kernel updates the page []

Difference between the fork() and vfork() system call?During the fork() system call the Kernel makes a copy of the parent processs address space and attaches it to the child process.But the vfork() system call do not makes any copy of the parents address space, so it is faster than the fork() system call. The child process as a result of the vfork() []

How the Kernel handles the fork() system call in traditional Unix and in the System V Unix, while swapping?Kernel in traditional Unix, makes the duplicate copy of the parents address space and attaches it to the childs process, while swapping. Kernel in System V Unix, manipulates the region tables, page table, and pfdata table entries, by incrementing the reference count of the region table of shared regions.

What are the requirements for a swapper to work?The swapper works on the highest scheduling priority. Firstly it will look for any sleeping process, if not found then it will look for the ready-to-run process for swapping. But the major requirement for the swapper to work the ready-to-run process must be core-resident for at least 2 seconds before swapping out. And for swapping []

What is Expansion swap?At the time when any process requires more memory than it is currently allocated, the Kernel performs Expansion swap. To do this Kernel reserves enough space in the swap device. Then the address translation mapping is adjusted for the new virtual address space but the physical memory is not allocated. At last Kernel swaps the []

What is Fork swap?fork() is a system call to create a child process. When the parent process calls fork() system call, the child process is created and if there is short of memory then the child process is sent to the read-to-run state in the swap device, and return to the user state without swapping the parent process. []

What are the entities that are swapped out of the main memory while swapping the process out of the main memory?All memory space occupied by the process, processs u-area, and Kernel stack are swapped out, theoretically.Practically, if the processs u-area contains the Address Translation Tables for the process then Kernel implementations do not swap the u-area.

Is the Process before and after the swap are the same? Give reason.Process before swapping is residing in the primary memory in its original form. The regions (text, data and stack) may not be occupied fully by the process, there may be few empty slots in any of the regions and while swapping Kernel do not bother about the empty slots while swapping the process outAfter swapping []

What are the events done by the Kernel after a process is being swapped out from the main memory?When Kernel swaps the process out of the primary memory, it performs the following:Kernel decrements the Reference Count of each region of the process. If the reference count becomes zero, swaps the region out of the main memory.Kernel allocates the space for the swapping process in the swap device.Kernel locks the other swapping process while []

What is major difference between the Historic Unix and the new BSD release of Unix System V in terms of Memory Management?Historic Unix uses Swapping entire process is transferred to the main memory from the swap device, whereas the Unix System V uses Demand Paging only the part of the process is moved to the main memory. Historic Unix uses one Swap Device and Unix System V allow multiple Swap Devices

What is an advantage of executing a process in background?The most common reason to put a process in the background is to allow you to do something else interactively without waiting for the process to complete. At the end of the command you add the special background symbol, &. This symbol tells your shell to execute the given command in the background.Example: cp *.* []

What Happens when you execute a program?When you execute a program on your UNIX system, the system creates a special environment for that program. This environment contains everything needed for the system to run the program as if no other program were running on the system. Each process has process context, which is everything that is unique about the state of []

What are the process states in Unix?As a process executes it changes state according to its circumstances. Unix processes have the following states:Running : The process is either running or it is ready to run .Waiting : The process is waiting for an event or for a resource.Stopped : The process has been stopped, usually by receiving a signal.Zombie : The []

What is a zombie?When a program forks and the child finishes before the parent, the kernel still keeps some of its information about the child in case the parent might need it - for example, the parent may need to check the childs exit status. To be able to get this information, the parent calls `wait(); In the []

How can a parent and child process communicate?A parent and child can communicate through any of the normal inter-process communication schemes (pipes, sockets, message queues, shared memory), but also have some special ways to communicate that take advantage of their relationship as a parent and child. One of the most obvious is that the parent can get the exit status of the []

How can you get/set an environment variable from a program?Getting the value of an environment variable is done by using `getenv().Setting the value of an environment variable is done by using `putenv().

Explain fork() system call.The `fork() used to create a new process from an existing process. The new process is called the child process, and the existing process is called the parent. We can tell which is which by checking the return value from `fork(). The parent gets the childs pid returned to him, but []

What are various IDs associated with a process?Unix identifies each process with a unique integer called ProcessID. The process that executes the request for creation of a process is called the parent process whose PID is Parent Process ID. Every process is associated with a particular user called the owner who has privileges over the process. The identification for the user is []

Brief about the initial process sequence while the system boots up.While booting, special process called the swapper or scheduler is created with Process-ID 0. The swapper manages memory allocation for processes and influences CPU allocation. The swapper inturn creates 3 children:the process dispatcher,vhand and dbflush with IDs 1,2 and 3 respectively.This is done by executing the file /etc/init. Process dispatcher gives birth to the shell. []

What is a shell?A shell is an interactive user interface to an operating system services that allows an user to enter commands as character strings or through a graphical user interface.The shell converts them to system calls to the OS or forks off a process to execute the command. System call results and other information from the OS []

How does the inode map to data block of a file?Inode has 13 block addresses. The first 10 are direct block addresses of the first 10 data blocks in the file. The 11th address points to a one-level index block. The 12th address points to a two-level (double in-direction) index block. The 13th address points to a three-level(triple in-direction)index block.This provides a very large maximum []

Discuss the mount and unmount system callsThe privileged mount system call is used to attach a file system to a directory of another file system; the unmount system call detaches a file system. When you mount another file system on to your directory, you are essentially splicing one directory tree onto a branch in another directory tree. The first argument to []

How do you create special files like named pipes and device files?The system call mknod creates special files in the following sequence.1. kernel assigns new inode,2. sets the file type to indicate that the file is a pipe, directory or special file,3. If it is a device file, it makes the other entries like major, minor device numbers.For example: If the device is a disk, major []

What are links and symbolic links in UNIX file system?A link is a second name (not a file) for a file. Links can be used to assign more than one name to a file, but cannot be used to assign a directory more than one name or link filenames on different computers.Symbolic link is a file that only contains the name of another file.Operation []

What are the Unix system calls for I/O?open(pathname,flag,mode) - open filecreat(pathname,mode) - create fileclose(filedes) - close an open fileread(filedes,buffer,bytes) - read data from an open filewrite(filedes,buffer,bytes) - write data to an open filelseek(filedes,offset,from) - position an open filedup(filedes) - duplicate an existing file descriptordup2(oldfd,newfd) - duplicate to a desired file descriptorfcntl(filedes,cmd,arg) - change properties of an open fileioctl(filedes,request,arg) - change the behaviour []

What Happens when you execute a program?When you execute a program on your UNIX system, the system creates a special environment for that program. This environment contains everything needed for the system to run the program as if no other program were running on the system. Each process has process context, which is everything that is unique about the state of []

What are the process states in Unix?As a process executes it changes state according to its circumstances. Unix processes have the following states:Running : The process is either running or it is ready to run .Waiting : The process is waiting for an event or for a resource.Stopped : The process has been stopped, usually by receiving a signal.Zombie : The []

What is a zombie?When a program forks and the child finishes before the parent, the kernel still keeps some of its information about the child in case the parent might need it - for example, the parent may need to check the childs exit status. To be able to get this information, the parent calls `wait(); In the []

How can a parent and child process communicate?A parent and child can communicate through any of the normal inter-process communication schemes (pipes, sockets, message queues, shared memory), but also have some special ways to communicate that take advantage of their relationship as a parent and child. One of the most obvious is that the parent can get the exit status of the []

How can you get/set an environment variable from a program?Getting the value of an environment variable is done by using `getenv().Setting the value of an environment variable is done by using `putenv().

Explain fork() system call.The `fork() used to create a new process from an existing process. The new process is called the child process, and the existing process is called the parent. We can tell which is which by checking the return value from `fork(). The parent gets the childs pid returned to him, but []

What are various IDs associated with a process?Unix identifies each process with a unique integer called ProcessID. The process that executes the request for creation of a process is called the parent process whose PID is Parent Process ID. Every process is associated with a particular user called the owner who has privileges over the process. The identification for the user is []

Brief about the initial process sequence while the system boots up.While booting, special process called the swapper or scheduler is created with Process-ID 0. The swapper manages memory allocation for processes and influences CPU allocation. The swapper inturn creates 3 children:the process dispatcher,vhand and dbflush with IDs 1,2 and 3 respectively.This is done by executing the file /etc/init. Process dispatcher gives birth to the shell. []

What is a shell?A shell is an interactive user interface to an operating system services that allows an user to enter commands as character strings or through a graphical user interface.The shell converts them to system calls to the OS or forks off a process to execute the command. System call results and other information from the OS []

How does the inode map to data block of a file?Inode has 13 block addresses. The first 10 are direct block addresses of the first 10 data blocks in the file. The 11th address points to a one-level index block. The 12th address points to a two-level (double in-direction) index block. The 13th address points to a three-level(triple in-direction)index block.This provides a very large maximum []

Discuss the mount and unmount system callsThe privileged mount system call is used to attach a file system to a directory of another file system; the unmount system call detaches a file system. When you mount another file system on to your directory, you are essentially splicing one directory tree onto a branch in another directory tree. The first argument to []

How do you create special files like named pipes and device files?The system call mknod creates special files in the following sequence.1. kernel assigns new inode,2. sets the file type to indicate that the file is a pipe, directory or special file,3. If it is a device file, it makes the other entries like major, minor device numbers.For example: If the device is a disk, major []

What is a FIFO?FIFO are otherwise called as named pipes. FIFO (first-in-first-out) is a special file which is said to be data transient. Once data is read from named pipe, it cannot be read again.Also, data can be read only in the order written. It is used in interprocess communication where a process writes to one end of []

What are links and symbolic links in UNIX file system?A link is a second name (not a file) for a file. Links can be used to assign more than one name to a file, but cannot be used to assign a directory more than one name or link filenames on different computers.Symbolic link is a file that only contains the name of another file.Operation []

What are the Unix system calls for I/O?open(pathname,flag,mode) - open filecreat(pathname,mode) - create fileclose(filedes) - close an open fileread(filedes,buffer,bytes) - read data from an open filewrite(filedes,buffer,bytes) - write data to an open filelseek(filedes,offset,from) - position an open filedup(filedes) - duplicate an existing file descriptordup2(oldfd,newfd) - duplicate to a desired file descriptorfcntl(filedes,cmd,arg) - change properties of an open fileioctl(filedes,request,arg) - change the behaviour []

Brief about the directory representation in UNIXs a file containing a correspondence between filenames and inodes. A directory is a special file that the kernel maintains. Only kernel modifies directories, but processes can read directories. The contents of a directory are a list of filename and inode number pairs. When new directories are created, kernel makes two entries []

What is inode?All UNIX files have its description stored in a structure called inode. The inode contains info about the file-size, its location, time of last access, time of last modification, permission and so on. Directories are also represented as files and have an associated inode. In addition to descriptions about the file, the inode contains pointers []

How are devices represented in UNIX?All devices are represented by files called special files that are locatedin/dev directory. Thus, device files and other files are named and accessed in the same way. A regular file is just an ordinary data file in the disk. A block special file represents a device with characteristics similar to a disk (data transfer []

Brief about the directory representation in UNIXA Unix directory is a file containing a correspondence between filenames and inodes. A directory is a special file that the kernel maintains. Only kernel modifies directories, but processes can read directories. The contents of a directory are a list of filename and inode number pairs. When new directories are created, kernel makes two entries []

What is inode?All UNIX files have its description stored in a structure called inode. The inode contains info about the file-size, its location, time of last access, time of last modification, permission and so on. Directories are also represented as files and have an associated inode. In addition to descriptions about the file, the inode contains pointers []

How are devices represented in UNIX?All devices are represented by files called special files that are locatedin/dev directory. Thus, device files and other files are named and accessed in the same way. A regular file is just an ordinary data file in the disk. A block special file represents a device with characteristics similar to a disk (data transfer []

How is the command $cat file2 different from $cat >file2

Answer The Commond $cat file in unix is used to display the content of the file and where as commond $cat >> file is to append the text to the end of the file without overwritting the information of the file. Incase if the file does not exist in the directory the commond will create a newfile in file system.

$cat >file means to create a new file $cat file means to open an existing file.

Answered By: selva,raviDate: 7/13/2007

cat > file it means creating file for file cat file it means used to display the file content

Explain the steps that a shell follows while processing a command.

Answer When processing a command the searchs for the utility for the command in the directories specified in the PATH varible and it in invokes that utility. That utility will execute the command with help of kernel and the output is given to shell. And then the displays out put to the user.

Explain the steps that a shell follows while processing a command.

Answer When processing a command the searchs for the utility for the command in the directories specified in the PATH varible and it in invokes that utility. That utility will execute the command with help of kernel and the output is given to shell. And then the displays out put to the user.

Which command is used to delete all files in the current directory and all its sub-directories?

Answer #rm -fr

# rm -rf *

Answered By: Amit ShiknisDate: 12/25/2007

rm -r *

What is the use of the command "ls -x chapter[1-5]"

Answer Yes you are correct. It stands for listing the files Chapter with suffix 1 to 5 but it will display the files in columns as with-x option.

How does the kernel differentiate device files and ordinary files?

Answer Device filles are of 2 types --- charcater device file and block device file

type field in the file's inode structure

b--- block device file

c--- character device file

How to switch to a super user status to gain privileges?

Answer Use su command. The system asks for password and when valid entry is made the user gains super user (admin) privileges.

What are shell variables?

Answer Shell variables are system environment variables.They include

TERM,SHELL, MAIL

the output of the shell variable we can see by typing the command

$>echo $TERM

ansi

at the prompt.

What is redirection?

Answer Redirection is a feature in Unix where the data from the standard out put or a file,so on.can be redirected i.e divert to a file or a program and vice versa.

> -- out put redirection

>> -- out put redirectin(appending at the last)

< -- input redirection

How to terminate a process which is running and the specialty on command kill 0?

Answer With the help of kill command we can terminate the process.Syntax: kill pidKill 0 - kills all processes in your system except the login shell.

How to terminate a process which is running and the specialty on command kill 0?

Answer With the help of kill command we can terminate the process.Syntax: kill pidKill 0 - kills all processes in your system except the login shell.

How to sfind free space in unix/linux

Answer Df and du commands are used for checking free space on disk .df -h or df -Humanreadable gives human readable format of free space.

What is the difference between soft link and hard link in unix operating system ?

Answer Hard Links :

1. All Links have same inode number.

2.ls -l command shows all the links with the link column(Second) shows No. of links.

3. Links have actual file contents

4.Removing any link ,just reduces the link count , but doesn't affect other links.

Soft Links(Symbolic Links) :

1.Links have different inode numbers.

2. ls -l command shows all links with second column value 1 and the link points to original file.

3. Link has the path for original file and not the contents.

4.Removing soft link doesn't affect anything but removing original file ,the link becomes "dangling" link which points to nonexistant file.

to concatenate (attach) two strings?

Answer For concatenating two string we use cat command.

Ex:- cat str1 str2

Explain the UNIX Kernel.

Answer UNIX Kernel is heart of the operating system. UNIX kernal is loaded first when UNIX system is booted. It handles allocation of devices, cpu, memory from that ponint on.

How many prompts are available in a UNIX system?

Answer Unix/ Linux Supports four Prompts PS1, PS2, PS3, PS4

#,@,$,% are 4 prompts

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