BASH/C2/Nested-and-multilevel-if-elsif-statements/English

Title of script: More on if loop in Bash Shell scripting

Author: Lavitha Pereira

Keywords: video tutorial, Bash shell, Nested if-else, Multilevel if-else

Visual Cue	Narration
Display Slide 1	Dear friends, Welcome to the spoken tutorial on More on if-loop in BASH Shell scripting
Display Slide 2	In the first part of this tutorial, we will learn the use of Nested if-else Multilevel if-else and few examples
Display Slide 3 Prerequisite spoken-tutorial.org	To follow this tutorial, You should be familiar with the Linux Operating System. If not, for relevant tutorials please visit spoken hyphen tutorial dot org.
Display Slide 4 System Requirements	For this tutorial I am using Ubuntu Linux 12.04 OS and GNU Bash version 4.1.10 GNU Bash version 4 or above is recommended to practice this tutorial.
Display Slide 5 Nested If-else <Flow graph>	Let us understand the flow of Nested If-else statement Here, if condition1 is true condition 2 is evaluated . If condition1 is false then statement 3 will be executed. If both the conditions are true , then statement 1 will be executed. And if condition 2 is false , then statement 2 will be executed
Open file On Terminal>> Type gedit nestedifelse.sh>> Press Enter	I will open an already typed program in the file nestedifelse.sh Go to Terminal and type gedit nestedifelse.sh Press Enter
	Let me explain the code now
#!/bin/bash	This is first line of bash shell script known as shebang line
NAME="anusha"	The variable NAME has the value anusha
PASSWORD="abc123"	The variable PASSWORD has the value abc123
read -p "Enter Name: " myname	The read command reads one line of data from standard input . -p flag displays Prompt. The string after -p which is “Enter name: ” will be displayed on the terminal. myname is a variable which stores the text entered by user during execution.
if [ "$myname" = "$NAME" ]; then	This statement compares two variables myname and NAME if the user enter the name “anusha” the condition will be true. It will now ask for the password.
read -s -p "Password:" mypassword	This reads and stores the entered password in variable mypassword. Here, -s flag is for silent mode. It means the text entered by the user will NOT be displayed on the terminal
Highlight if [ "$mypassword" = "$PASSWORD" ]; then	This statement compare variable mypassword and PASSWORD if the value of variable mypassword matches with value of PASSWORD The condition will be true and it will display Welcome on the screen
echo -e "\nWelcome"	This displays message Welcome on the terminal if password matches -e enables interpretation of backslash escapes \n stands for new line. It means the string Welcome will be printed on the next line.
else echo -e "\nWrong password"	If the condition to match password is false, it will display Wrong password on the screen This displays message Wrong password
fi	This ends the inner if loop
else echo "Wrong name"	This statement is called if the condition to match name is false. It displays message Wrong Name
fi	This ends the outer if loop
Switch to Terminal>> Type chmod +x nestedifelse.sh>> press Enter>> Type ./nestedifelse>> press Enter	Now switch to the terminal, to make it executable type chmod space plus x space nestedifelse.sh and press Enter Now type dot slash nestedifelse.sh and Press Enter
	The program verifies for two conditions i.e. Name and Password when it is executed on the terminal
Output [Highlight] Enter Name: anusha Password: abc123	Here, the prompt displays Enter Name: Now let us enter anusha As condition is true, Next condition will be evaluated. Now the prompt says Password: I will type password as abc123 As the password matches with already declared variable PASSWORD. Prompt displays the message as Welcome
Press up arrow key>> go to ./nestedifelse.sh>> Press Enter	Now let us execute the script again. Press the up arrow key. Go to B./nestedifelse.sh and press Enter But this time we will enter same name, but wrong password.
Highlight Output Enter Name: >>type swathi>> Press Enter	Now I will enter the name swathi and Press enter It is displayed Wrong name As name enter swathi will not match the previously declared value anusha. The control comes out of if loop and prints the else statement which is Wrong name
Display slide 6 Multilevel if-else <Flow graph>	if condition1 is true then statement1 is executed If condition1 is false condition 2 is executed if condition2 is true then statement 2 is executed And if condition 2 is false then condition N is evaluated. If condition N is true then statement N is executed And if Condition N is false then statement X is executed.
On Terminal>> Type gedit multilevel-iflese.sh>> Press enter	Let us understand the flow with the help of a bash script I will open already typed program. I will open the file multilevel-ifelse.sh using the command gedit multilevel-ifelse.sh and Press Enter
	This program illustrates whether the entered string is Empty. Or it will check whether it has words raj or jit in it.
	Let me explain the code now
#!/bin/bash	This is first line of bash shell script known as shebang line
read -p "Enter a word : " string	The read command reads one line of data from standard input. -p display the prompt with string “Enter a word” string is a variable which stores the word entered by user during execution.
if [ -z "$string" ]; then echo " Nothing is Entered "	-z checks whether the variable string is empty Type man test on terminal and explore different string comparison. This statement will be printed if nothing was entered.
elif [[ "$string" == *"raj"* ]]; then echo "\”$string\” contains word raj"	Checks whether entered string contains the word raj If yes, it displays message as $string contains the word raj
elif [[ $string = *"jit"* ]]; then echo "\”$string\” contains word jit"	Checks whether entered string contains the word jit If yes, it displays message as $string contains word jit
else echo "Sorry! entered word does not contain either raj or jit"	If the entered string does not contain either raj or jit Then it displays the message Sorry! entered word does not contain either raj or jit
fi	End of multilevel if-else loop Let us execute the program
On the terminal >> Type chmod +x multilevel-ifesle.sh>> Press Enter >> Type ./multilevel-ifelse.sh>> Press enter	Switch to the terminal First make the file executable type: chmod space plus x space multilevel-ifelse.sh Now type dot slash multilevel-ifelse.sh and Press Enter
	It takes input from the user. Let us understand with different inputs.
Highlight The output Enter a Word: echo " Nothing was entered"	I will Press Enter without typing anything. The first condition in Multilevel if-else is satisfied. It will display: Nothing was entered and Control comes out of Multilevel if-else loop.
Go to ./multilevel.sh by Pressing up arrow key>> Press Enter Highlight Type: abhijit “abijit” contains word 'jit'. elif [[ $string = *"jit"* ]]; then	Now let us try executing the script with different Name. Press up arrow key The prompt displays as Enter a word: I will enter as abijit The output is: “abijit” contains word 'jit'. The control flows to third condition The first two condition does not match and display message.
	The same logic is applicable for all conditions. Try executing the program with input string which has raj .
Display Slide 7 Summary	Summary In this tutorial we learnt, the usage of Nested If-else in a script which verifies Name and Password of a user We also saw usage of Multilevel if-else in a script with does a String comparison
Display Slide 8 Assignment	# As an assignment, write a program to output different messages when number is greater than 3, lesser than 3 or equal to 3 and if the user input is empty
Display Slide 9	Watch the video available at the link shown below It summarizes the Spoken Tutorial project If you do not have good bandwidth, you can download and watch it
Display Slide 10 Spoken Tutorial Workshops	The Spoken Tutorial Project Team Conducts workshops using spoken tutorials Gives certificates to those who pass an online test For more details, please write to contact@spoken-tutorial.org
Display Slide 11 Acknowledgement	Spoken Tutorial Project is a part of the Talk to a Teacher project It is supported by the National Mission on Education through ICT, MHRD, Government of India More information on this Mission is available at: http://spoken-tutorial.org/NMEICT-Intro
Display Slide 12	The script has been contributed by Lavitha Pereira This is Ashwini from IIT Bombay. Thank you for joining.

Contributors and Content Editors

Ashwini, Nancyvarkey