1 what does the variable do Give an example where this valu

1. what does the variable $? do? Give an example where this value is useful, and explain whether it is case-sensitive or not. (Justify your Answers with example by running commands in the Linux machine).

2. Why does echo, $MyVar, quotes, set, unset, $PS1, $PATH, env, export commands are used, give a detailed explanation of it and also Plz run all the commands in the Linux machine. (Everyone should have their own Id’s).

Solution

1. Dollar sign($) is one of the important character generally used in languages which these are used to devolep applications. This dollar sign is a case sensitive and itis followed with the variable so that it shows the value that is present in the variable.

Let us see the example of it wher we use

[rahul@RHELv4u3 ~]$ echo This is the $SHELL shell

This is the /bin/bash shell. we can take this example.

[rahul@RHELv4u3 ~]$ echo Hello $USER

Hello rahul.............. This shows that this is a case sensitive.

2. echo: This command is used to display the value which is present in the variable

example:

#!/bin/sh

MY_MESSAGE=\"Hello World\"

echo $MY_MESSAGE

$MyVar: This command is used to find the functionality of the variable

example:

#!/bin/sh

echo \"MYVAR is: $MYVAR\"

MYVAR=\"hi there\"

echo \"MYVAR is: $MYVAR\"

quotes: The double quotes which allows parsing of the variables whereas single quotes stops from this.

Let us take an example of this:

[rahul@RHELv4u3 ~]$ MyVar=555

[rahul@RHELv4u3 ~]$ echo $MyVar

555

[rahul@RHELv4u3 ~]$ echo \"$MyVar\"

555

[rahul@RHELv4u3 ~]$ echo \'$MyVar\'

$MyVar

These variables are replaced with with their own values in double quotes in bash shell

rahul@laika:~$ city=hyderabad

rahul@laika:~$ echo \"We are in $city today.\"

We are in hyderabad today.

rahul@laika:~$ echo \'We are in $city today.\'

We are in $city today.

set: This command is used to show the environmental variables.

unset: This command is to removce the variables from environmental shell.

example:

[rahul@RHEL4b ~]$ MyVar=6602

[rahul @RHEL4b ~]$ echo $MyVar

6602

[rahul @RHEL4b ~]$ unset MyVar

[rahul @RHEL4b ~]$ echo $MyVar

[rahul @RHEL4b ~]$

$PS1: this commnad is used to finds the shell prompt that you are using

example:

rahul@deb503:~$ PS1=prompt

prompt

promptPS1=\'prompt \'

prompt

prompt PS1=\'> \'

>

> PS1=\'\\u@\\h$ \'

rahul @deb503$

rahul @deb503$ PS1=\'\\u@\\h:\\W$\'

rahul @deb503:~$

$PATH; This command is used to find the shell to tell that what command it is looking to execute.

evample:

[[rahul@RHEL4b ~]$ echo $PATH

/usr/kerberos/bin:/usr/local/bin:/bin:/usr/bin:

env: This command is used to display the exported values list.

example:

[rahul@RHEL4b ~]$ bash -c \'echo $SHELL $HOME $USER\'

/bin/bash /home/ rahul rahul

[rahul @RHEL4b ~]$ env -i bash -c \'echo $SHELL $HOME $USER\'

/bin/bash

[rahul @RHEL4b ~]$

this command is also used to clean the shell

export: This command is used to export the commands to other shells.

example:

[rahul@RHEL4b ~]$ var3=three

[rahul @RHEL4b ~]$ var4=four

[rahul @RHEL4b ~]$ export var4

[rahul @RHEL4b ~]$ echo $var3 $var4

three four

[rahul @RHEL4b ~]$ bash

[rahul @RHEL4b ~]$ echo $var3 $var4

four