Difference between revisions of "BASH/C2/Nested-and-multilevel-if-elsif-statements/English-timed"

| Dear friends, welcome to the spoken tutorial on '''Nested and multilevel if statement''' in '''BASH.'''

|  In this tutorial, we will learn about: 

| '''Multilevel if-else statement'''.

| If not, for relevant tutorials, please visit our website which is as shown

|  For this tutorial, I am using  

| Here, if '''condition 1''' is '''True''' then '''condition 2''' will be evaluated,

|  if '''condition2''' is '''True''' then''' statement 1''' will be executed.

| That means, only when both the''' conditions''' 1 and 2 are '''True''' then''' statement 1''' will be executed.

| If''' condition1''' is '''False, '''then''' statement 3''' will be executed.

| And, if''' condition 2''' is '''False''' then''' statement 2''' will be executed.

| I have written code in the file '''nestedifelse.sh'''.

| The variable '''PASSWORD '''has been assigned the value "abc123".

| '- (hyphen) p' '''flag''' displays the '''prompt'''.  

| The '''string''' after - (hyphen) p, “Enter name: ” will be displayed on the '''terminal'''.  

| The first '''if''' statement compares the two variables '''myname '''and '''NAME '''

| i.e. the user input and the value stored in variable''' Name '''i.e. "anusha".

| If the two values match then the rest of the code in this '''if''' statement will be evaluated.

| The '''read''' command reads and stores the entered password in variable '''mypassword'''.

| Here, '- (hyphen) s' '''flag''' is for''' silent mode. '''

| It means, the text entered by the user will not be displayed on the '''terminal.'''

| Here, we have another set of '''if-else statements'''.

|  This set of '''if-else statements '''is nested within the first '''if '''.

| '''echo''' displays the message''' “Welcome” '''on the '''terminal '''when the '''if''' '''condition''' is '''True'''

| '-e' enables interpretation of '''backslash escape'''.

| '\n' stands for '''new line''' which means the string '''Welcome” '''will be printed on a new line.

|  When the '''if''' condition is not '''True''' then the '''else''' condition will be executed  

| i.e. when the passwords don't match, the '''else''' condition will be executed.

| In this case, '''echo''' displays ''' “Wrong password”'''.

|  '''fi '''ends the inner ''' if-else''' statement.

| Coming back to our first '''if-else statement-'''

| if the values in '''myname''' and '''NAME''' don't match then this '''else''' statement will be executed.

|  '''fi '''ends the outer''' if-else''' statement.

|  Now, open the '''terminal window''' by pressing '''ctrl+alt''' and '''t''' keys simultaneously on your keyboard.

|  Type: '''dot slash nestedifelse.sh'''

| i.e '''Name''' and '''Password'''

|  Here, the '''prompt''' displays '''Enter Name:'''

|  Let us type "anusha".

|  As this '''condition '''is '''True''', the next '''if''' condition will be evaluated.

|  Now the '''prompt '''says '''Password'''.

|  I will type the password as "abc123".

|  The password matches with the value in the variable '''PASSWORD.'''

|  So, the prompt displays the message '''Welcome'''.

| | Press the 'up-arrow' key.  

|  This time, we will enter the same name with different password.

|  So, I will enter the name as "anusha" and password as "123".

|  Let's '''execute''' the '''script''' once more.

| This time, we will give the name as "swati".

| This is because the name "swati" does not match the previously declared value "anusha".

| The '''control''' comes out of the first '''if''' statement and executes the '''else''' statement.

| If '''condition1''' is '''True''' then '''statement1''' is executed.

| If '''condition1''' is '''False''' then''' condition 2''' is evaluated.

| 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''' will be executed.

| The '''if''' condition checks whether input string is '''null.'''

|'- (hyphen) z' checks whether length of '''string''' is '''zero.'''

|Type: '''man test ''' on '''terminal '''and explore various '''string ''' comparison.  

|  This '''echo''' statement  will be printed if nothing is entered.

|  The first '''elif''' condition checks whether the''' input string''' contains "raj".

|If it does then this '''echo''' statement will be printed.

|The '''wildcard character '''ensures that any word with "raj" in it, will be identified.

|  The next '''elif''' condition checks whether the''' input string''' contains the word "jit".

|If it does then this '''echo''' statement will be printed.

| The '''else''' condition will be executed when all the above conditions fail.

|And it will display the message '''Sorry! Input does not contain either 'raj' or 'jit'. '''

|  '''fi''' indicates the end of ''' multilevel if-else''' statement.

|  Let us '''execute''' the program.

|And the '''control''' comes out of the '''multilevel if-else statement.'''

| Let me clear the '''prompt'''.

|Press 'up-arrow' key.

|I will type "abhijit".

|  The output displayed is: '''“abhijit" contains word 'jit'.'''

|This shows that the '''control''' flowed to the third '''condition''' in our code.

|The first two conditions did not match.

| The same logic is applicable for all the conditions.

|Let us summarize.

|In this tutorial, we learned the usage of:

| '''Nested if-else:''' with ''' Name''' and''' Password''' verification and

|'''Multilevel if-else: '''String comparison''' program.

|* greater than 3

|* lesser than 3

|* or equal to 3

|or when the user input is empty.

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|It summarizes the Spoken Tutorial project.

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