Difference between revisions of "BASH/C2/Logical-Operators/English-timed"

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{| border=1  
 
{| border=1  
−
|'''Time'''
+
|   Time  
−
|'''Narration'''
+
|   Narration  
 
|-
 
|-
 
|  00:01
 
|  00:01
−
|  Dear friends, welcome to the Spoken tutorial on '''Logical Operators''' in '''Bash'''.
+
|  Dear friends, welcome to the Spoken tutorial on   Logical Operators   in   Bash   .
  
 
|-
 
|-
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|-
 
|-
 
|00:10
 
|00:10
−
|'''Logical AND'''
+
|   Logical AND  
−
'''Logical OR'''
+
  Logical OR  
−
'''Logical NOT'''using a few examples.  
+
  Logical NOT   using a few examples.  
  
 
|-
 
|-
Line 22: Line 22:
 
|-
 
|-
 
|  00:22
 
|  00:22
−
|'''if-else statement'''
+
|   if-else statement  
−
'''command line arguments '''and  
+
  command line arguments   and  
−
'''quoting '''in''' BASH.'''
+
  quoting   in   BASH.  
  
 
|-
 
|-
Line 36: Line 36:
 
|-
 
|-
 
|  00:38
 
|  00:38
−
| '''Ubuntu Linux 12.04''' OS  
+
|     Ubuntu Linux 12.04   OS  
  
 
|-
 
|-
 
|  00:43
 
|  00:43
−
| '''GNU Bash''' version '''4.1.10'''
+
|   GNU Bash   version   4.1.10  
  
 
|-
 
|-
 
|  00:47
 
|  00:47
−
| '''GNU Bash''' version 4 or above is recommended for practice.
+
|   GNU Bash   version 4 or above is recommended for practice.
  
 
|-
 
|-
 
|    00:53
 
|    00:53
−
|  Let us understand the use of ''' Logical-operators.'''
+
|  Let us understand the use of     Logical-operators.  
  
 
|-
 
|-
 
|    00:57
 
|    00:57
−
| '''Logical operators''' are mainly used to control program flow.
+
|   Logical operators   are mainly used to control program flow.
  
 
|-
 
|-
 
|    01:02
 
|    01:02
−
| '''Logical operators''' help to link two expressions or '''conditions'''.
+
|   Logical operators   help to link two expressions or   conditions   .
  
 
|-
 
|-
 
|  01:09
 
|  01:09
−
| They can be a part of '''if, while''' or some other '''control statements'''.
+
| They can be a part of   if, while   or some other   control statements   .
  
 
|-
 
|-
 
|  01:15
 
|  01:15
−
|  Let's see the syntax of '''logical AND'''.
+
|  Let s see the syntax of   logical AND   .
  
 
|-
 
|-
 
|  01:19
 
|  01:19
−
| '''Opening square-bracket space dollar symbol condition1 space closing square-bracket space ampersand ampersand space opening square-bracket space dollar symbol condition2 space closing square-bracket.'''
+
|   Opening square-bracket space dollar symbol condition1 space closing square-bracket space ampersand ampersand space opening square-bracket space dollar symbol condition2 space closing square-bracket.  
 
|-
 
|-
 
|  01:38
 
|  01:38
Line 75: Line 75:
 
|-
 
|-
 
|  01:41
 
|  01:41
−
| ''' Opening square-bracket space dollar symbol condition1 space hyphen-a space dollar symbol condition2 space closing square-bracket.'''
+
|     Opening square-bracket space dollar symbol condition1 space hyphen-a space dollar symbol condition2 space closing square-bracket.  
  
 
|-
 
|-
 
|  01:53
 
|  01:53
−
| '''Logical AND''' returns '''True''' when both '''condition1''' and '''condition2''' are '''True'''.
+
|     Logical AND   returns   True   when both   condition1   and   condition2   are   True   .
  
 
|-
 
|-
 
|  02:00
 
|  02:00
−
|  Let us see the syntax of '''Logical OR'''.
+
|  Let us see the syntax of   Logical OR   .
  
 
|-
 
|-
 
|  02:04
 
|  02:04
−
|   '''Opening square-bracket space dollar symbol condition1 space closing square-bracket space vertical bar again vertical bar space opening square-bracket space dollar symbol condition2 space closing square-bracket.'''
+
|     Opening square-bracket space dollar symbol condition1 space closing square-bracket space vertical bar again vertical bar space opening square-bracket space dollar symbol condition2 space closing square-bracket.  
  
 
|-
 
|-
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|-
 
|-
 
|  02:24
 
|  02:24
−
| '''Opening square-bracket space dollar symbol condition1 space hyphen-o space dollar symbol condition2 space closing square-bracket.'''
+
|   Opening square-bracket space dollar symbol condition1 space hyphen-o space dollar symbol condition2 space closing square-bracket.  
  
 
|-
 
|-
 
|  02:36
 
|  02:36
−
| '''Logical OR''' returns ''' True''' when either '''condition1''' or '''condition2''' is '''True'''.
+
|   Logical OR   returns     True   when either   condition1   or   condition2   is   True   .
 
|-
 
|-
 
|  02:43   
 
|  02:43   
−
|  Let us learn the usage of ''' Logical OR''' and '''Logical AND''' using an example.
+
|  Let us learn the usage of     Logical OR   and   Logical AND   using an example.
  
 
|-
 
|-
 
|  02:50   
 
|  02:50   
−
|  I have already typed the '''code''' in a file named '''logical.sh'''.
+
|  I have already typed the   code   in a file named   logical.sh   .
  
 
|-
 
|-
 
|  02:55   
 
|  02:55   
−
|  Open the '''terminal''' by pressing '''ctrl+alt''' and '''t''' keys simultaneously on your keyboard.
+
|  Open the   terminal   by pressing   ctrl+alt   and   t   keys simultaneously on your keyboard.
  
 
|-
 
|-
 
|  03:04   
 
|  03:04   
−
| Type: '''gedit space logical.sh space ampersand''' sign, press '''Enter.'''
+
| Type:   gedit space logical.sh space ampersand   sign, press   Enter.  
  
 
|-
 
|-
Line 122: Line 122:
 
|-
 
|-
 
| 03:18     
 
| 03:18     
−
| Let me explain the '''code''' now.
+
| Let me explain the   code   now.
  
 
|-
 
|-
 
|  03:21   
 
|  03:21   
−
|  This is the '''shebang line.'''
+
|  This is the   shebang line.  
  
 
|-
 
|-
 
| 03:25   
 
| 03:25   
−
|  The '''read '''command reads one line of data from ''' standard input.'''
+
|  The   read   command reads one line of data from     standard input.  
  
 
|-
 
|-
 
| 03:29   
 
| 03:29   
−
| '''- (hyphen) p''' displays the '''prompt.'''
+
|   - (hyphen) p   displays the   prompt.  
  
 
|-
 
|-
 
| 03:33   
 
| 03:33   
−
| '''string''' is a '''variable''' which stores the text entered by the user, during execution.
+
|   string   is a   variable   which stores the text entered by the user, during execution.
  
 
|-
 
|-
 
|  03:39  
 
|  03:39  
−
|    The '''if''' statement checks whether the entered '''string''' is '''empty.'''
+
|    The   if   statement checks whether the entered   string   is   empty.  
 
|-
 
|-
 
|  03:45  
 
|  03:45  
−
| '''- (hyphen) z '''checks whether length of '''string''' is zero.
+
|   - (hyphen) z   checks whether length of   string   is zero.
  
 
|-
 
|-
 
|    03:50   
 
|    03:50   
−
|    Type: '''man space test''' on ''' terminal''' to explore various other '''string''' comparisons.  
+
|    Type:   man space test   on     terminal   to explore various other   string   comparisons.  
  
 
|-
 
|-
 
|  03:57     
 
|  03:57     
−
|  The '''echo''' '''statement''' will print a message if nothing was entered.
+
|  The   echo       statement   will print a message if nothing was entered.
  
 
|-
 
|-
 
| 04:02   
 
| 04:02   
−
|  If the '''string''' is not empty, the program will move to the first '''elif statement.'''
+
|  If the   string   is not empty, the program will move to the first   elif statement.  
  
 
|-
 
|-
 
| 04:08   
 
| 04:08   
−
| Here, it checks whether the entered '''string''' contains both the words  "raj" and  "jit".
+
| Here, it checks whether the entered   string   contains both the words  "raj" and  "jit".
  
 
|-
 
|-
Line 169: Line 169:
 
|-
 
|-
 
| 04:20
 
| 04:20
−
| Please note that '''logical AND''' is used here.
+
| Please note that   logical AND   is used here.
  
 
|-
 
|-
Line 177: Line 177:
 
|-
 
|-
 
|  04:31  
 
|  04:31  
−
| If that is not so then the program will move onto the second '''elif statement.'''
+
| If that is not so then the program will move onto the second   elif statement.  
  
 
|-
 
|-
 
| 04:37  
 
| 04:37  
−
| Here, it checks whether the entered '''string''' contains either "raj" or "jit".
+
| Here, it checks whether the entered   string   contains either "raj" or "jit".
  
 
|-
 
|-
 
| 04:43  
 
| 04:43  
−
| If 'yes' then it displays the message.
+
| If yes then it displays the message.
  
 
|-
 
|-
 
| 04:47  
 
| 04:47  
−
| Please note that '''logical OR''' is used here.
+
| Please note that   logical OR   is used here.
  
 
|-
 
|-
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|-
 
|-
 
|  04:59   
 
|  04:59   
−
|  Lastly, we have the default '''else statement.'''
+
|  Lastly, we have the default   else statement.  
  
 
|-
 
|-
 
| 05:02
 
| 05:02
−
| When all the above statements are '''False''' then this statement will be executed.
+
| When all the above statements are   False   then this statement will be executed.
  
 
|-
 
|-
 
|  05:08   
 
|  05:08   
−
| '''"fi"''' is the end of '''multilevel if-else''' '''loop'''.
+
|     "fi"   is the end of   multilevel if-else       loop   .
  
 
|-
 
|-
 
|  05:12   
 
|  05:12   
−
| Let us '''execute''' the program.
+
| Let us   execute   the program.
  
 
|-
 
|-
 
|  05:15  
 
|  05:15  
−
| Switch back to the '''terminal.'''
+
| Switch back to the   terminal.  
  
 
|-
 
|-
 
|  05:17  
 
|  05:17  
−
| First make the file executable by typing- '''chmod space plus x space logical dot sh''' press '''Enter'''.
+
| First make the file executable by typing-   chmod space plus x space logical dot sh   press   Enter   .
 
|-
 
|-
 
|  05:30  
 
|  05:30  
−
| Now type: '''dot slash logical.sh''' press '''Enter.'''
+
| Now type:   dot slash logical.sh   press   Enter.  
  
 
|-
 
|-
 
|  05:36   
 
|  05:36   
−
| The prompt displays '''"Enter a word:" '''
+
| The prompt displays   "Enter a word:"  
  
 
|-
 
|-
 
|  05:38   
 
|  05:38   
−
| I will enter''' "jitinraj" '''.
+
| I will enter   "jitinraj"   .
  
 
|-
 
|-
 
|  05:42   
 
|  05:42   
−
| The output is:''' "jitinraj contains both the words 'raj' and 'jit' ".'''
+
| The output is:   "jitinraj contains both the words raj and jit ".  
  
 
|-
 
|-
 
|  05:48   
 
|  05:48   
−
| This means that the '''control''' was passed to the second '''statement'''.
+
| This means that the   control   was passed to the second   statement   .
  
 
|-
 
|-
 
|  05:52   
 
|  05:52   
−
| And as both the '''conditions''' are satisfied, it displays the message.
+
| And as both the   conditions   are satisfied, it displays the message.
  
 
|-
 
|-
 
|  05:57
 
|  05:57
−
|  Now, let us '''execute''' the '''script''' again.
+
|  Now, let us   execute   the   script   again.
  
 
|-
 
|-
 
|  06:00
 
|  06:00
−
| Press the '''up-arrow''' key.  
+
| Press the   up-arrow   key.  
  
 
|-
 
|-
 
|  06:02
 
|  06:02
−
| Go to '''./logical.sh ''' press '''Enter'''.
+
| Go to   ./logical.sh     press   Enter   .
  
 
|-
 
|-
 
| 06:07   
 
| 06:07   
−
|  The prompt displays '''"Enter a word:"'''
+
|  The prompt displays   "Enter a word:"  
  
 
|-
 
|-
 
| 06:09   
 
| 06:09   
−
| This time I will enter '''"abhijit".'''
+
| This time I will enter   "abhijit".  
  
 
|-
 
|-
 
| 06:13   
 
| 06:13   
−
| The output is displayed as: '''"abhijit contains the word 'raj' or 'jit'".'''
+
| The output is displayed as:   "abhijit contains the word raj or jit ".  
  
 
|-
 
|-
 
|  06:19  
 
|  06:19  
−
|  Please try executing the program with different inputs and observe the '''output'''.
+
|  Please try executing the program with different inputs and observe the   output   .
  
 
|-
 
|-
 
|  06:25  
 
|  06:25  
−
|  Let's switch back to our '''slides'''.  
+
|  Let s switch back to our   slides   .  
  
 
|-
 
|-
 
|  06:27
 
|  06:27
−
|  Let's have a look at '''logical NOT''' operator.  
+
|  Let s have a look at   logical NOT   operator.  
  
 
|-
 
|-
 
|  06:31
 
|  06:31
−
|  It inverts the '''Boolean''' value of an expression  
+
|  It inverts the   Boolean   value of an expression  
  
 
|-
 
|-
 
|  06:35
 
|  06:35
−
|  which means, it returns '''True''' if the expression is '''False'''
+
|  which means, it returns   True   if the expression is   False  
  
 
|-
 
|-
 
|  06:40
 
|  06:40
−
|  and returns '''False''' if the expression is '''True'''.
+
|  and returns   False   if the expression is   True   .
  
 
|-
 
|-
 
|  06:44
 
|  06:44
−
|  The syntax of '''logical NOT''' operator is-
+
|  The syntax of   logical NOT   operator is-
  
 
|-
 
|-
 
|  06:48
 
|  06:48
−
| '''Exclamation mark space expression'''
+
|   Exclamation mark space expression  
  
 
|-
 
|-
 
|  06:52
 
|  06:52
−
| or '''opening square-bracket space exclamation mark space expression space closing square-bracket.'''
+
| or     opening square-bracket space exclamation mark space expression space closing square-bracket.  
  
 
|-
 
|-
Line 308: Line 308:
 
|-
 
|-
 
|  07:03
 
|  07:03
−
| I have already typed the '''code''' in a file.
+
| I have already typed the   code   in a file.
  
 
|-
 
|-
 
|  07:05
 
|  07:05
−
| So, I will go to the '''terminal ''' and type: '''gedit space logicalNOT dot sh space ampersand''' sign, press ''' Enter.'''
+
| So, I will go to the   terminal     and type:   gedit space logicalNOT dot sh space ampersand   sign, press     Enter.  
  
 
|-
 
|-
 
|  07:18
 
|  07:18
−
|  Now type the code as shown here, in your '''logicalNOT dot sh''' file.
+
|  Now type the code as shown here, in your   logicalNOT dot sh   file.
  
 
|-
 
|-
 
| 07:24  
 
| 07:24  
−
|  This is the ''' shebang line '''as we already know.
+
|  This is the     shebang line   as we already know.
  
 
|-
 
|-
 
|  07:28
 
|  07:28
−
| '''$1''' is the first '''command line argument''' passed to the '''script'''.
+
|     $1   is the first   command line argument   passed to the   script   .
  
 
|-
 
|-
 
|  07:33
 
|  07:33
−
| '''- (hyphen) f''' checks if the file exists with the same name that was passed as an '''argument'''.
+
|   - (hyphen) f   checks if the file exists with the same name that was passed as an   argument   .
  
 
|-
 
|-
 
|  07:41
 
|  07:41
−
| So, it will return '''True''' if the file exists and '''False''' if it does not exist.
+
| So, it will return   True   if the file exists and   False   if it does not exist.
  
 
|-
 
|-
 
|  07:48
 
|  07:48
−
|  This '''NOT operator''' here, inverses the returned value
+
|  This   NOT operator   here, inverses the returned value
  
 
|-
 
|-
 
|  07:52
 
|  07:52
−
| which means, if a file of that name exists, the condition will be '''True.'''
+
| which means, if a file of that name exists, the condition will be   True.  
  
 
|-
 
|-
 
|  07:58
 
|  07:58
−
| But the '''NOT operator''' will inverse its value to '''False'''.  
+
| But the   NOT operator   will inverse its value to   False   .  
  
 
|-
 
|-
 
|  08:02
 
|  08:02
−
| And it will display the message '''"FILE does not exist"'''.
+
| And it will display the message   "FILE does not exist"   .
  
 
|-
 
|-
 
|  08:07   
 
|  08:07   
−
| Here, in the '''else statement,''' it displays the message '''FILE exists'''.
+
| Here, in the   else statement,   it displays the message     FILE exists   .
 
   
 
   
 
|-
 
|-
 
| 08:13
 
| 08:13
−
| '''"fi"''' marks the end of '''if loop.'''
+
|     "fi"   marks the end of   if loop.  
  
 
|-
 
|-
 
|  08:16
 
|  08:16
−
|  Now , switch to the '''terminal'''.   
+
|  Now , switch to the   terminal   .   
  
 
|-
 
|-
 
|  08:18
 
|  08:18
−
| Let me clear the '''prompt'''.
+
| Let me clear the   prompt   .
  
 
|-
 
|-
 
|  08:20
 
|  08:20
−
| Let's create an empty file with the name '''test.txt'''.
+
| Let s create an empty file with the name   test.txt   .
  
 
|-
 
|-
 
|  08:25
 
|  08:25
−
| Type : '''touch space test dot txt''' press '''Enter.'''
+
| Type :   touch space test dot txt   press   Enter.  
  
 
|-
 
|-
 
| 08:32  
 
| 08:32  
 
|  Next, make the script executable by typing:
 
|  Next, make the script executable by typing:
−
'''chmod space plus x space logicalNOT dot sh''' press '''Enter.'''
+
  chmod space plus x space logicalNOT dot sh   press   Enter.  
  
 
|-
 
|-
 
| 08:45  
 
| 08:45  
−
| Now, type: '''dot slash logicalNOT dot sh space test dot txt''' press ''' Enter.'''
+
| Now, type:   dot slash logicalNOT dot sh space test dot txt   press     Enter.  
  
 
|-
 
|-
 
| 08:55   
 
| 08:55   
−
|  Our '''shell script''' will check whether the file exists.
+
|  Our   shell script   will check whether the file exists.
  
 
|-
 
|-
 
| 09:00   
 
| 09:00   
−
| Our file '''test dot txt ''' exists,  hence the value will be '''True.'''
+
| Our file   test dot txt     exists,  hence the value will be   True.  
  
 
|-
 
|-
 
| 09:07   
 
| 09:07   
−
| Then the '''logical NOT''' will inverse that value and return '''False.'''
+
| Then the   logical NOT   will inverse that value and return   False.  
  
 
|-
 
|-
 
| 09:12   
 
| 09:12   
−
| Because the evaluation is '''False''', the '''else statement''' is evaluated.
+
| Because the evaluation is   False   , the   else statement   is evaluated.
  
 
|-
 
|-
 
|  09:18  
 
|  09:18  
−
|  And the message displayed is -'''File 'test.txt' exists'''.
+
|  And the message displayed is -   File test.txt exists   .
  
 
|-
 
|-
 
|  09:23
 
|  09:23
−
| Try executing the program again with '''argument''' '''test1.txt'''.  
+
| Try executing the program again with   argument       test1.txt   .  
  
 
|-
 
|-
Line 413: Line 413:
 
|-
 
|-
 
| 09:33
 
| 09:33
−
|  Come back to our '''slides'''.  Let us summarize.
+
|  Come back to our   slides   .  Let us summarize.
  
 
|-
 
|-
 
| 09:37
 
| 09:37
 
| In this tutorial, we learned the usage of:  
 
| In this tutorial, we learned the usage of:  
−
'''logical AND'''
+
  logical AND  
−
'''logical OR '''and
+
  logical OR   and
−
'''logical NOT'''.
+
  logical NOT   .
  
 
|-
 
|-
Line 436: Line 436:
 
|-
 
|-
 
| 09:51
 
| 09:51
−
| using '''logical operators '''  explained in this tutorial.
+
| using   logical operators     explained in this tutorial.
  
 
|-
 
|-
 
| 09:56
 
| 09:56
−
| (Hint: '''man space test''')
+
| (Hint:   man space test   )
  
 
|-
 
|-
Line 472: Line 472:
 
|-
 
|-
 
| 10:26
 
| 10:26
−
|   '''Spoken Tutorial''' Project is a part of the '''Talk to a Teacher''' project.
+
|     Spoken Tutorial   Project is a part of the   Talk to a Teacher   project.
  
 
|-
 
|-

Latest revision as of 15:09, 16 October 2017

Time Narration
00:01 Dear friends, welcome to the Spoken tutorial on Logical Operators in Bash .
00:07 In this tutorial, we will learn use of:
00:10 Logical AND 
  Logical OR   
  Logical NOT   using a few examples.
00:19 To follow this tutorial, you should have knowledge of:
00:22 if-else statement 
  command line arguments    and 
  quoting    in    BASH.
00:30 If not, for relevant tutorials, please visit our website which is as shown.
00:36 For this tutorial, I am using:
00:38 Ubuntu Linux 12.04 OS
00:43 GNU Bash version 4.1.10
00:47 GNU Bash version 4 or above is recommended for practice.
00:53 Let us understand the use of Logical-operators.
00:57 Logical operators are mainly used to control program flow.
01:02 Logical operators help to link two expressions or conditions .
01:09 They can be a part of if, while or some other control statements .
01:15 Let s see the syntax of logical AND .
01:19 Opening square-bracket space dollar symbol condition1 space closing square-bracket space ampersand ampersand space opening square-bracket space dollar symbol condition2 space closing square-bracket.
01:38 Or we can use this syntax-
01:41 Opening square-bracket space dollar symbol condition1 space hyphen-a space dollar symbol condition2 space closing square-bracket.
01:53 Logical AND returns True when both condition1 and condition2 are True .
02:00 Let us see the syntax of Logical OR .
02:04 Opening square-bracket space dollar symbol condition1 space closing square-bracket space vertical bar again vertical bar space opening square-bracket space dollar symbol condition2 space closing square-bracket.
02:22 Or we can use this syntax-
02:24 Opening square-bracket space dollar symbol condition1 space hyphen-o space dollar symbol condition2 space closing square-bracket.
02:36 Logical OR returns True when either condition1 or condition2 is True .
02:43 Let us learn the usage of Logical OR and Logical AND using an example.
02:50 I have already typed the code in a file named logical.sh .
02:55 Open the terminal by pressing ctrl+alt and t keys simultaneously on your keyboard.
03:04 Type: gedit space logical.sh space ampersand sign, press Enter.
03:12 Now type the code as shown here, in your "logical.sh" file.
03:18 Let me explain the code now.
03:21 This is the shebang line.
03:25 The read command reads one line of data from standard input.
03:29 - (hyphen) p displays the prompt.
03:33 string is a variable which stores the text entered by the user, during execution.
03:39 The if statement checks whether the entered string is empty.
03:45 - (hyphen) z checks whether length of string is zero.
03:50 Type: man space test on terminal to explore various other string comparisons.
03:57 The echo statement will print a message if nothing was entered.
04:02 If the string is not empty, the program will move to the first elif statement.
04:08 Here, it checks whether the entered string contains both the words "raj" and "jit".
04:16 If yes, then it echoes out a message.
04:20 Please note that logical AND is used here.
04:24 Hence, the message will be displayed only when both the conditions are satisfied.
04:31 If that is not so then the program will move onto the second elif statement.
04:37 Here, it checks whether the entered string contains either "raj" or "jit".
04:43 If yes then it displays the message.
04:47 Please note that logical OR is used here.
04:52 The message will be displayed only when any one of the conditions are satisfied.
04:59 Lastly, we have the default else statement.
05:02 When all the above statements are False then this statement will be executed.
05:08 "fi" is the end of multilevel if-else loop .
05:12 Let us execute the program.
05:15 Switch back to the terminal.
05:17 First make the file executable by typing- chmod space plus x space logical dot sh press Enter .
05:30 Now type: dot slash logical.sh press Enter.
05:36 The prompt displays "Enter a word:"
05:38 I will enter "jitinraj" .
05:42 The output is: "jitinraj contains both the words raj and jit ".
05:48 This means that the control was passed to the second statement .
05:52 And as both the conditions are satisfied, it displays the message.
05:57 Now, let us execute the script again.
06:00 Press the up-arrow key.
06:02 Go to ./logical.sh press Enter .
06:07 The prompt displays "Enter a word:"
06:09 This time I will enter "abhijit".
06:13 The output is displayed as: "abhijit contains the word raj or jit ".
06:19 Please try executing the program with different inputs and observe the output .
06:25 Let s switch back to our slides .
06:27 Let s have a look at logical NOT operator.
06:31 It inverts the Boolean value of an expression
06:35 which means, it returns True if the expression is False
06:40 and returns False if the expression is True .
06:44 The syntax of logical NOT operator is-
06:48 Exclamation mark space expression
06:52 or opening square-bracket space exclamation mark space expression space closing square-bracket.
07:00 Let us see an example.
07:03 I have already typed the code in a file.
07:05 So, I will go to the terminal and type: gedit space logicalNOT dot sh space ampersand sign, press Enter.
07:18 Now type the code as shown here, in your logicalNOT dot sh file.
07:24 This is the shebang line as we already know.
07:28 $1 is the first command line argument passed to the script .
07:33 - (hyphen) f checks if the file exists with the same name that was passed as an argument .
07:41 So, it will return True if the file exists and False if it does not exist.
07:48 This NOT operator here, inverses the returned value
07:52 which means, if a file of that name exists, the condition will be True.
07:58 But the NOT operator will inverse its value to False .
08:02 And it will display the message "FILE does not exist" .
08:07 Here, in the else statement, it displays the message FILE exists .
08:13 "fi" marks the end of if loop.
08:16 Now , switch to the terminal .
08:18 Let me clear the prompt .
08:20 Let s create an empty file with the name test.txt .
08:25 Type : touch space test dot txt press Enter.
08:32 Next, make the script executable by typing: 
  chmod space plus x space logicalNOT dot sh    press    Enter.
08:45 Now, type: dot slash logicalNOT dot sh space test dot txt press Enter.
08:55 Our shell script will check whether the file exists.
09:00 Our file test dot txt exists, hence the value will be True.
09:07 Then the logical NOT will inverse that value and return False.
09:12 Because the evaluation is False , the else statement is evaluated.
09:18 And the message displayed is - File test.txt exists .
09:23 Try executing the program again with argument test1.txt .
09:29 And observe the control flow as explained before.
09:33 Come back to our slides . Let us summarize.
09:37 In this tutorial, we learned the usage of: 
  logical AND   
  logical OR    and
  logical NOT   .
09:45 As an assignment,
09:47 check whether the file exists
09:49 and is executable
09:51 using logical operators explained in this tutorial.
09:56 (Hint: man space test )
09:59 Watch the video available at the link shown below.
10:02 It summarizes the Spoken-Tutorial project.
10:05 If you do not have good bandwidth, you can download and watch it.
10:09 The Spoken Tutorial Project team:
10:12 Conducts workshops using spoken tutorials.
10:15 Gives certificates to those who pass an online test.
10:19 For more details, please write to contact@spoken-tutorial.org
10:26 Spoken Tutorial Project is a part of the Talk to a Teacher project.
10:30 It is supported by the National Mission on Education through ICT, MHRD, Government of India.
10:37 More information on this mission is available at the link shown below.
10:42 The script has been contributed by FOSSEE and spoken-tutorial team.
10:47 This is Ashwini Patil from IIT Bombay, signing off.
10:51 Thank you for joining.

Contributors and Content Editors

PoojaMoolya, Pratik kamble, Ranjana, Sandhya.np14, Yogananda.india

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