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

9. List the types of shells 10. List 11. How do I use the following sings? Give an example on how to use thesm all the ways to communicate with another user who is using the system Page 3 of 4 1466 words %2F0

9. List the types of shells 10. List 11. How do I use the following sings? Give an example on how to use thesm all the ways to communicate with another user who is using the system Page 3 of 4 1466 words %2F0

Expert Answer


Types of shells:


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.


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


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.


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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