Difference between revisions of "BASH/C2/Conditional-Loops/English-timed"

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(Created page with "'''Title of script:''' '''Basic If loop in BASH ''' '''Author:''' Ashwini Patil '''Keywords: video tutorial, for loop, while loop''' {| border=1 !Time !Narration |- | 00:0...")
 
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|  Let us start with an introduction to ''' loops'''
 
|  Let us start with an introduction to ''' loops'''
  
 
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| '''Loops''' are used to execute a group of statements repeatedly.
 
| '''Loops''' are used to execute a group of statements repeatedly.
  
 
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|  Let us see the syntax.
 
|  Let us see the syntax.
  
 
|-
 
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| '''for expression 1, 2, 3'''
 
| '''for expression 1, 2, 3'''
  
 
|-
 
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| '''statement 1, 2, 3'''
 
| '''statement 1, 2, 3'''
  
 
|-
 
|-
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| 00:51
 
| And this is the end of '''for loop'''.
 
| And this is the end of '''for loop'''.
  
 
|-
 
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| 00:55
 
|  An alternate syntax of '''for loop '''is:
 
|  An alternate syntax of '''for loop '''is:
  
 
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| '''for variable in sequence/range'''
 
| '''for variable in sequence/range'''
  
 
|-
 
|-
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| 01:03
 
| '''statement 1, 2, 3'''
 
| '''statement 1, 2, 3'''
  
 
|-
 
|-
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| 01:06
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| 01:06
 
| And end of '''for loop'''.
 
| And end of '''for loop'''.
  
 
|-
 
|-
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| 01:09
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| 01:09
 
|    Let us see an example of '''for loop''' using the first syntax.
 
|    Let us see an example of '''for loop''' using the first syntax.
  
 
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| 01:14
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| In this program, we will calculate the sum of first '''n''' numbers.
 
| In this program, we will calculate the sum of first '''n''' numbers.
 
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| 01:20  
 
|  Note that our filename is '''for.sh'''
 
|  Note that our filename is '''for.sh'''
  
 
|-
 
|-
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| 01: 25  
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| 01:25  
 
|  This is our '''shebang line'''.
 
|  This is our '''shebang line'''.
  
 
|-
 
|-
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| 01: 28
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| 01:28
 
|  The variable '''number''' will store the value given by user.  
 
|  The variable '''number''' will store the value given by user.  
  
 
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|-
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|  01:34
 
| The value is an integer here.
 
| The value is an integer here.
  
 
|-
 
|-
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|  01:37
 
| Now, we initialize the variable '''sum''' as zero.
 
| Now, we initialize the variable '''sum''' as zero.
  
 
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|-
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|  01:42  
 
|  This is where we begin the '''for loop.'''
 
|  This is where we begin the '''for loop.'''
  
 
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|-
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| 01:45  
 
| First, we initialize '''i''' to '''1'''.
 
| First, we initialize '''i''' to '''1'''.
  
 
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|-
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| 01: 48  
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| 01:48  
 
| Then we check whether '''i''' is less than or equal to '''number'''.
 
| Then we check whether '''i''' is less than or equal to '''number'''.
  
 
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|  Now here, we calculate the '''sum''' as '''sum plus I'''.
 
|  Now here, we calculate the '''sum''' as '''sum plus I'''.
  
 
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|  02:00
 
| and then we print it.
 
| and then we print it.
  
 
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|-
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| 02: 03   
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| 02:03   
 
|  After this, we increment the value of '''i''' by '''1'''.
 
|  After this, we increment the value of '''i''' by '''1'''.
  
 
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| 02:08
 
|  And then we check the condition till this condition is '''false'''.
 
|  And then we check the condition till this condition is '''false'''.
 
|-
 
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|  On exiting the '''for loop,''' this message is printed.
 
|  On exiting the '''for loop,''' this message is printed.
  
 
|-
 
|-
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|  02: 19
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|  02:19
 
|  Let us execute the program and observe what happens.
 
|  Let us execute the program and observe what happens.
  
 
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|-
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| 02:24   
 
|  On the '''terminal''' type - '''chmod +x for.sh'''
 
|  On the '''terminal''' type - '''chmod +x for.sh'''
  
 
|-
 
|-
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| 02: 31   
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| 02:31   
 
| Then type: '''./for.sh'''
 
| Then type: '''./for.sh'''
  
 
|-
 
|-
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|  02: 36   
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|  02:36   
 
|  I will enter '''5''' as the input number.
 
|  I will enter '''5''' as the input number.
  
 
|-
 
|-
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|  02:40   
 
| The '''sum''' that is calculated for each value of '''I''' is displayed.
 
| The '''sum''' that is calculated for each value of '''I''' is displayed.
  
 
|-
 
|-
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|  02: 46   
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|  02:46   
 
| After that, the last line of the output is displayed:
 
| After that, the last line of the output is displayed:
  
 
|-
 
|-
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|  02: 50
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|  02:50
 
| '''Sum of first n numbers is 15'''
 
| '''Sum of first n numbers is 15'''
  
 
|-
 
|-
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|  02: 54
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|  02:54
 
| Now let us see the flow of the program.
 
| Now let us see the flow of the program.
  
 
|-
 
|-
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|  02: 57
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|  02:57
 
| Let me resize the windows.
 
| Let me resize the windows.
  
 
|-
 
|-
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|  03:00
 
|  First we have value of '''i''' as '''1'''.
 
|  First we have value of '''i''' as '''1'''.
  
 
|-
 
|-
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|  03:04  
 
|  Then we check whether ''' 1 ''' is less than or equal to ''' 5.'''
 
|  Then we check whether ''' 1 ''' is less than or equal to ''' 5.'''
  
 
|-
 
|-
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|  03: 10
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|  03:10
 
| Since the condition is '''true,''' we calculate '''sum''' as ''' 0 + 1.'''
 
| Since the condition is '''true,''' we calculate '''sum''' as ''' 0 + 1.'''
  
 
|-
 
|-
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|  03: 16
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|  03:16
 
| Now we have '''sum '''as '''1.'''
 
| Now we have '''sum '''as '''1.'''
  
 
|-
 
|-
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|  03: 20
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|  03:20
 
| Then we print '''sum ''' i.e '''1.'''
 
| Then we print '''sum ''' i.e '''1.'''
  
 
|-
 
|-
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|   03: 24  
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| 03:24  
 
|  Next, '''I''' is incremented by '''1''' and the new value of ''' i ''' is ''' 2.'''
 
|  Next, '''I''' is incremented by '''1''' and the new value of ''' i ''' is ''' 2.'''
  
 
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|-
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|   03: 31  
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| 03:31  
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| Then we check whether ''' 2 ''' is less than or equal to ''' 5.'''
+
| Then we check whether ''' 2 ''' is less than or equal to ''' 5.'''
  
 
|-
 
|-
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|  03: 36  
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|  03:36  
 
| The condition is '''true''' and now sum will be ''' 1 + 2 ''' i.e ''' 3.'''
 
| The condition is '''true''' and now sum will be ''' 1 + 2 ''' i.e ''' 3.'''
  
 
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|-
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|   03: 44
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| 03:44
 
|    '''i ''' is then incremented by '''1''' and then the new value of ''' i''' is ''' 3.'''
 
|    '''i ''' is then incremented by '''1''' and then the new value of ''' i''' is ''' 3.'''
  
 
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| 03: 51
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| 03:51
 
| And we get '''sum''' as ''' 6.'''
 
| And we get '''sum''' as ''' 6.'''
  
 
|-
 
|-
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| 03: 55  
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| 03:55  
 
|  The script will continue to add the next value of ''' I ''' to the previous value in ''' sum.'''
 
|  The script will continue to add the next value of ''' I ''' to the previous value in ''' sum.'''
  
 
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| 04: 02  
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| 04:02  
 
| This will continue till '''<nowiki>i<=5</nowiki> is false.'''
 
| This will continue till '''<nowiki>i<=5</nowiki> is false.'''
  
 
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| 04: 09  
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|  On exiting the '''for loop,''' the final message is printed.
 
|  On exiting the '''for loop,''' the final message is printed.
  
 
|-
 
|-
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| 04: 14   
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| 04:14   
 
|  Let us see another example of '''for loop'''using the second syntax.
 
|  Let us see another example of '''for loop'''using the second syntax.
  
 
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| 04: 20   
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| 04:20   
 
| I have written the code in this file and named it as '''for-loop.sh'''
 
| I have written the code in this file and named it as '''for-loop.sh'''
  
 
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| 04: 27   
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| 04:27   
 
| This simple program will list the files in a directory.
 
| This simple program will list the files in a directory.
  
 
|-
 
|-
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| 04: 32  
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| 04:32  
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| This is the '''shebang line.'''
+
| This is the '''shebang line.'''
  
 
|-
 
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| 04: 35  
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| 04:35  
 
|  Then we have '''for loop'''.
 
|  Then we have '''for loop'''.
  
 
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| 04:37  
 
| '''ls''' command lists the directory content.
 
| '''ls''' command lists the directory content.
  
 
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| 04: 41  
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| '''-1 (hyphen one)''' lists one file per line.
 
| '''-1 (hyphen one)''' lists one file per line.
  
 
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| 04: 46  
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| 04:46  
 
| This will list all the files present in your home directory.
 
| This will list all the files present in your home directory.
  
 
|-
 
|-
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|  04: 51  
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|  04:51  
 
| This is the end of '''for loop.'''
 
| This is the end of '''for loop.'''
  
 
|-
 
|-
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| 04: 53
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| 04:53
 
|  Let us execute the script on the '''terminal''' by typing -  
 
|  Let us execute the script on the '''terminal''' by typing -  
  
 
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| 04: 58
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| 04:58
 
| '''chmod +x for-loop.sh'''
 
| '''chmod +x for-loop.sh'''
  
 
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| 05: 04
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| 05:04
 
| '''./for-loop.sh'''
 
| '''./for-loop.sh'''
  
 
|-
 
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| 05: 09
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| 05:09
 
|  This will display all the files present in the '''Home''' directory.
 
|  This will display all the files present in the '''Home''' directory.
  
 
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| 05: 14   
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| 05:14   
 
|  Now, we will learn about ''' while loop.'''
 
|  Now, we will learn about ''' while loop.'''
  
 
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|-
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| 05: 18   
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| 05:18   
 
| Let us understand the syntax first.
 
| Let us understand the syntax first.
  
 
|-
 
|-
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| 05: 21  
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| 05:21  
 
|  '''while condition'''
 
|  '''while condition'''
 
'''statement 1, 2, 3'''
 
'''statement 1, 2, 3'''
Line 290: Line 290:
  
 
|-
 
|-
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|   05: 27
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| 05:27
 
| This means that the '''while loop''' will execute as long as the condition is '''true.'''
 
| This means that the '''while loop''' will execute as long as the condition is '''true.'''
  
 
|-
 
|-
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| 05: 34
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|05:34
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|   Let us see an example of '''while loop.'''
+
|Let us see an example of '''while loop.'''
  
 
|-
 
|-
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|  05: 37
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|  05:37
 
| Here I have named it as '''while.sh'''
 
| Here I have named it as '''while.sh'''
  
 
|-
 
|-
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|  05: 42
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|  05:42
 
| In this program, we will calculate the sum of even numbers within a given range.
 
| In this program, we will calculate the sum of even numbers within a given range.
  
 
|-
 
|-
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|   05: 49
+
|05: 49
 
|  Let us go through the code.
 
|  Let us go through the code.
  
 
|-
 
|-
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| 05: 52
+
|05:52
 
| Here, we accept a number from the user and store it in variable '''number'''.
 
| Here, we accept a number from the user and store it in variable '''number'''.
  
 
|-
 
|-
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| 05: 59
+
|05:59
 
|  Next, we declare variables '''i''' and '''sum''' and initialize them to ''' 0 (zero).'''
 
|  Next, we declare variables '''i''' and '''sum''' and initialize them to ''' 0 (zero).'''
  
 
|-
 
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| 06: 06
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|06:06
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|   Now this is the '''while condition.'''
+
|Now this is the '''while condition.'''
  
 
|-
 
|-
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| 06: 08
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| 06:08
 
| Here we check whether '''i''' is '''less than or equal''' to value of '''number''' given by the user.
 
| Here we check whether '''i''' is '''less than or equal''' to value of '''number''' given by the user.
  
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| This will ensure that we only add the even numbers.
 
| This will ensure that we only add the even numbers.
  
 
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|  06:33  
 
| And the while loop is repeated till the value of '''i''' exceeds the value of '''number.'''
 
| And the while loop is repeated till the value of '''i''' exceeds the value of '''number.'''
 
|-
 
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|  06: 40  
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|  06:40  
 
|  When we exit the '''while loop, '''we print the sum of all the even numbers within the given range.
 
|  When we exit the '''while loop, '''we print the sum of all the even numbers within the given range.
  
 
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|   06:47  
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| 06:47  
 
| Let us execute the program.
 
| Let us execute the program.
  
 
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| 06:50  
 
|  Type on the '''terminal''':
 
|  Type on the '''terminal''':
  
 
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| 06:52  
 
| '''chmod +x while.sh'''
 
| '''chmod +x while.sh'''
  
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|  Then we check if '''2''' is less than or equal to '''15'''.
 
|  Then we check if '''2''' is less than or equal to '''15'''.
  

Revision as of 11:37, 8 December 2014

Title of script: Basic If loop in BASH Author: Ashwini Patil Keywords: video tutorial, for loop, while loop

Time Narration
00:01 Dear friends, welcome to the spoken tutorial on loops in BASH.
00:07 In this tutorial, we will learn
00:09 * for loop
00:11 * while loop
with a few examples
00:15 To record this tutorial I am using,
00:18 * Ubuntu Linux 12.04 Operating System
00:22 * GNU BASH version 4.1.10
00:26 Please note,GNU bash version 4 or above is recommended to practice this tutorial.
00:34 Let us start with an introduction to loops
00:37 Loops are used to execute a group of statements repeatedly.
00:43 Let us see the syntax.
00:45 for expression 1, 2, 3
00:49 statement 1, 2, 3
00:51 And this is the end of for loop.
00:55 An alternate syntax of for loop is:
00:58 for variable in sequence/range
01:03 statement 1, 2, 3
01:06 And end of for loop.
01:09 Let us see an example of for loop using the first syntax.
01:14 In this program, we will calculate the sum of first n numbers.
01:20 Note that our filename is for.sh
01:25 This is our shebang line.
01:28 The variable number will store the value given by user.
01:34 The value is an integer here.
01:37 Now, we initialize the variable sum as zero.
01:42 This is where we begin the for loop.
01:45 First, we initialize i to 1.
01:48 Then we check whether i is less than or equal to number.
01:54 Now here, we calculate the sum as sum plus I.
02:00 and then we print it.
02:03 After this, we increment the value of i by 1.
02:08 And then we check the condition till this condition is false.
02:14 On exiting the for loop, this message is printed.
02:19 Let us execute the program and observe what happens.
02:24 On the terminal type - chmod +x for.sh
02:31 Then type: ./for.sh
02:36 I will enter 5 as the input number.
02:40 The sum that is calculated for each value of I is displayed.
02:46 After that, the last line of the output is displayed:
02:50 Sum of first n numbers is 15
02:54 Now let us see the flow of the program.
02:57 Let me resize the windows.
03:00 First we have value of i as 1.
03:04 Then we check whether 1 is less than or equal to 5.
03:10 Since the condition is true, we calculate sum as 0 + 1.
03:16 Now we have sum as 1.
03:20 Then we print sum i.e 1.
03:24 Next, I is incremented by 1 and the new value of i is 2.
03:31 Then we check whether 2 is less than or equal to 5.
03:36 The condition is true and now sum will be 1 + 2 i.e 3.
03:44 i is then incremented by 1 and then the new value of i is 3.
03:51 And we get sum as 6.
03:55 The script will continue to add the next value of I to the previous value in sum.
04:02 This will continue till i<=5 is false.
04:09 On exiting the for loop, the final message is printed.
04:14 Let us see another example of for loopusing the second syntax.
04:20 I have written the code in this file and named it as for-loop.sh
04:27 This simple program will list the files in a directory.
04:32 This is the shebang line.
04:35 Then we have for loop.
04:37 ls command lists the directory content.
04:41 -1 (hyphen one) lists one file per line.
04:46 This will list all the files present in your home directory.
04:51 This is the end of for loop.
04:53 Let us execute the script on the terminal by typing -
04:58 chmod +x for-loop.sh
05:04 ./for-loop.sh
05:09 This will display all the files present in the Home directory.
05:14 Now, we will learn about while loop.
05:18 Let us understand the syntax first.
05:21 while condition

statement 1, 2, 3 End of while loop.

05:27 This means that the while loop will execute as long as the condition is true.
05:34 Let us see an example of while loop.
05:37 Here I have named it as while.sh
05:42 In this program, we will calculate the sum of even numbers within a given range.
05: 49 Let us go through the code.
05:52 Here, we accept a number from the user and store it in variable number.
05:59 Next, we declare variables i and sum and initialize them to 0 (zero).
06:06 Now this is the while condition.
06:08 Here we check whether i is less than or equal to value of number given by the user.
06:17 Then we calculate the sum by adding value of i to value of sum.
06:24 Next, we increment the value of i with 2.
06:28 This will ensure that we only add the even numbers.
06:33 And the while loop is repeated till the value of i exceeds the value of number.
06:40 When we exit the while loop, we print the sum of all the even numbers within the given range.
06:47 Let us execute the program.
06:50 Type on the terminal:
06:52 chmod +x while.sh
06:56 ./while.sh
07:00 I will give 15 as my input.
07:04 The last line of the output is:
07:06 Sum of even numbers within the given range is 56.
07:11 Let me resize the window and explain the output.
07:14 First we check whether i which is 0, is less than or equal to the number, which is 15.
07:24 The condition is true, hence sum will be 0+0 I.e 0.
07:31 Now i will be incremented by 2 and the new value of i is 2.
07:37 Then we check if 2 is less than or equal to 15.
07:43 The condition again is true; so we add 0+2.
07:49 Now sum has the value 2.
07:52 Again the value of i will be incremented by 2.
07:56 So now value of i will be 2+2 I.e 4.
08:03 And the next value of sum will be 4+2 I.e 6.
08:09 In the same way, the script will continue to add 2 to the previous value of i, till it exceeds 15.
08:18 And we get the total value in sum as 56.
08:24 This brings us to the end of this tutorial.
08:27 Let us summarize
08:28 In this tutorial we learnt two different syntax of for loop and we also learnt about the while loop.
08:37 As an assignment -
08:38 Find the sum of the first "n" prime numbers.
08:43 Watch the video available at the link shown below
08:46 It summarises the Spoken Tutorial project
08:50 If you do not have good bandwidth, you can download and watch it
08:54 The Spoken Tutorial Project Team
08:56 Conducts workshops using spoken tutorials
09:00 Gives certificates to those who pass an online test
09:04 For more details, please write to contact@spoken-tutorial.org
09:11 Spoken Tutorial Project is a part of the Talk to a Teacher project
09:14 It is supported by the National Mission on Education through ICT, MHRD, Government of India
09:22 More information on this Mission is available at the link shown below.
09:28 The script has been contributed by Fossee and spoken-tutorial team.
09:34 This is Ashwini Patil from IIT Bombay signning off.
09:38 Thank You for joining.

Contributors and Content Editors

PoojaMoolya, Pratik kamble, Ranjana, Sandhya.np14

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