BASH/C2/Logical-Operators/English-timed - Revision history

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PoojaMoolya at 10:50, 5 December 2014

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Ranjana: Created page with "'''Title of script''': Logical Operators in Bash '''Author:''' Lavitha pereira '''Keywords: Video tutorial, Bash Shell, Logical AND, Logical OR, Logical NOT''' {| border=1 !..."

2014-11-21T06:48:42Z

Created page with "'''Title of script''': Logical Operators in Bash '''Author:''' Lavitha pereira '''Keywords: Video tutorial, Bash Shell, Logical AND, Logical OR, Logical NOT''' {| border=1 !..."

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'''Title of script''': Logical Operators in Bash
'''Author:''' Lavitha pereira
'''Keywords: Video tutorial, Bash Shell, Logical AND, Logical OR, Logical NOT'''

{| border=1
!Time
!Narration
|-
| 00:01
| Dear friends, Welcome to the Spoken tutorial on '''Logical Operators in Bash '''

|-
| 00:07
| In this tutorial, we will learn

|-
| 00:10
| * Use of '''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''' helps 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''' an '''t''' keys simultaneousely on your keyboard.

|-
| 03:04
| Type: '''gedit space logical.sh space & 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''' display 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 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.sh space ampersand sign''' Press ''' Enter.'''

|-
| 07:18
| Now type the code as shown here in your '''logicalNOT.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 conditon 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.txt''' press ''' Enter.'''

|-
| 08:55
| Our shell script will check whether the file exists.

|-
| 09:00
| Our file '''test.txt ''' exists <nowiki>;</nowiki>''' 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 learnt 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 signning off.

|-
| 10:51
| Thank you for joining.

|}

@@ Line 446: / Line 446: @@
 | 09:56
 | (Hint: '''man space test''')
 |-

@@ Line 1: / Line 1: @@
 {| border=1
-!Time
+|'''Time'''
-!Narration
+|'''Narration'''
 |-
 |  00:01

@@ Line 1: / Line 1: @@
 {| border=1
 !Time
@@ Line 8: / Line 4: @@
 |-
 |  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'''.
 |-
-|   00:07
+| 00:07
-|  In this tutorial, we will learn use of:
+| In this tutorial, we will learn use of:
 |-
-|   00:10
+|00:10
-|* '''Logical AND'''
+|'''Logical AND'''
-* '''Logical OR'''
+'''Logical OR'''
-* '''Logical NOT'''
+'''Logical NOT'''using a few examples.
 using a few examples.
 |-
@@ Line 27: / Line 22: @@
 |-
 |  00:22
-|* '''if-else statement'''
+|'''if-else statement'''
-* '''command line arguments '''and
+'''command line arguments '''and
-* '''quoting '''in''' BASH.'''
+'''quoting '''in''' BASH.'''
 |-
@@ Line 41: / Line 36: @@
 |-
 |  00:38
-| * '''Ubuntu Linux 12.04''' OS
+|  '''Ubuntu Linux 12.04''' OS
 |-
 |  00:43
-| * '''GNU Bash''' version '''4.1.10'''
+| '''GNU Bash''' version '''4.1.10'''
 |-
@@ Line 423: / Line 418: @@
 | 09:37
 | In this tutorial, we learned the usage of:
-* '''logical AND'''
+'''logical AND'''
-* '''logical OR '''and
+'''logical OR '''and
-* '''logical NOT'''.
+'''logical NOT'''.
 |-
@@ Line 465: / Line 460: @@
 |-
 |  10:12
-|* Conducts workshops using spoken tutorials.
+|Conducts workshops using spoken tutorials.
 |-
 |  10:15
-|* Gives certificates to those who pass an online test.
+|Gives certificates to those who pass an online test.
 |-

@@ Line 73: / Line 73: @@
 |-
 |   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
@@ Line 80: / Line 80: @@
 |-
 |   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.'''
 |-
@@ Line 92: / Line 92: @@
 |-
 |  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.'''
 |-
@@ Line 100: / Line 100: @@
 |-
 |  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.'''
 |-
@@ Line 301: / Line 301: @@
 |-
 |  06:48
-| Exclamation mark space '''expression'''
+| '''Exclamation mark space expression'''
 |-
 |  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 237: / Line 237: @@
 |-
 |  05:42
-| The output is: ''jitinraj contains both the words raj and jit'''
+| The output is: '''jitinraj contains both the words raj and jit'''
 |-
@@ Line 305: / Line 305: @@
 |-
 |  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 317: / Line 317: @@
 |-
 |  07:05
-| So, I will go to the '''terminal ''' and type '''gedit space logicalNOT.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
-|  Now type the code as shown here in your '''logicalNOT.sh''' file.
+|  Now type the code as shown here in your '''logicalNOT dot sh''' file.
 |-
@@ Line 386: / Line 386: @@
 |-
 | 08:45
-| Now type '''dot slash logicalNOT dot sh space test.txt''' press ''' Enter.'''
+| Now type '''dot slash logicalNOT dot sh space test dot txt''' press ''' Enter.'''
 |-
@@ Line 394: / Line 394: @@
 |-
 | 09:00
-| Our file '''test.txt ''' exists <nowiki>;</nowiki>''' hence the value will be ''' true.'''
+| Our file '''test dot txt ''' exists  hence the value will be ''' true.'''
 |-
@@ Line 406: / Line 406: @@
 |-
 |  09:18
-|   And the message displayed is -
+|   And the message displayed is -'''File 'test.txt' exists'''
 '''File 'test.txt' exists'''
 |-