(Homework Solution): 9. List the types of shells 10. List 11. How do I use the following sings? Give an

Types of shells:

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There are various types of shells available in unix. They are listed below:

1. Bourne Shell (sh):

Bourne Shell is the original Unix shell written by Steve Bourne. It was written in the Bell Labs.

2. C Shell (csh):

C Shell provides a C-like language with which to write shell scripts and hence the name is C-SHELL

3. TC Shell (tcsh):

TC shell is available in the public domain. It has all the features of the C shell tand also emacs style editing of the command line.

4. Korn Shell (Ksh):

Korn shell was written by David Korn of Bell labs. It is now provided as the standard shell on Unix systems.

5. Bourne Again SHell (BASH):

Bash is written by Brian Fox for the GNU Project as a free software replacement for the Bourne shell.

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Ways to communicate with another user who is using the same system

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In the system, by default, accepting messages are turned off. This is for the security reasons. You must allow other users to send you message. Use the following command: mesg y

(1). Using WRITE command:

write username [terminal]

example: write pts/1 “Hello Brother.!!”

The above command will make the user using pts/1 to see a message “Hello Brother.!!”

(2). Using echo Command:

From terminal pts/1:

$ sudo echo “Good Mrng Brother” > /dev/pts/4

The above command will make the user using pts/4 to see the message “Good Mrng Brother.!!”

(3) Using wall command:

we can use this command to send a message to all the users.

$ sudo wall -n Hello

Everyone using the system will see hello message but they don’t know who sent the message because we use -n flag here. If you remove -n flag, everyone will know that it’s you.

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Using a semicolon ( ; ):

It is used as the command seperator. It seperates various commands in a single line.

example: $ echo “hello” ; echo “hai”

Here, the shell waits for each command to terminate.The return status is the exit status of the last command executed.

Using parenthesis () :

$(…) means execute the command in the parenthesis in a subshell and return its standard output.

Example: $ echo “Current Date is $(date)”

Using Ampersand (&):

It indicates the command runs in background.

Example: $ sh xyz.sh &

It executes the xyz.sh script in the background. With & the process starts in the background, so you can continue to use the shell and do not have to wait until the script is finished.

Using single quotes ( ‘ ‘ ):

It is used to indicate a string. They are called Strong Quotes.

example: $ echo ‘a b’

The output will be ‘a b’ it is a string.

Using backslah ( ):

It is called single character quote.

If you want to place text on two or more lines for readability, but the program expects one line, you need a line continuation character, we can use the backslash as the last character on the line:

example: $ echo This is

. a very

. Long line.

Using Double Quotes (” “):

These are called weak quotes.

we can use $ echo “hai”

We use these to have QUOTES WITHIN QUOTES.

$ echo ” I can’t go without you dear”

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