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

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'''Title of script''': Logical Operators in Bash
+
Title of script: Logical Operators in Bash
  
'''Author:''' Lavitha pereira
+
Author: Lavitha pereira
  
'''Keywords: Video tutorial, Bash Shell, Logical AND, Logical OR, Logical NOT'''
+
Keywords: Video tutorial, Bash Shell, Logical AND, Logical OR, Logical NOT
 
+
 
+
{| style="border-spacing:0;"
+
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Visual Cue
+
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Narration
+
  
 +
{| border="1"
 +
!width="50%"| <center>Visual Cue</center>
 +
!width="50%"| <center>Narration</center>
 
|-
 
|-
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide  
+
|Display Slide
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Dear friends, Welcome to the Spoken tutorial on
+
|Dear friends, Welcome to the Spoken tutorial on
  
 
'''Logical Operators in Bash '''
 
'''Logical Operators in Bash '''
 
 
|-
 
|-
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide  
+
|Display Slide
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| In this tutorial, we will learn
+
|In this tutorial, we will learn
 
+
* Use of '''Logical AND'''
+
* '''Logical OR'''
+
* '''Logical NOT operators'''
+
* using a few examples
+
 
+
 
+
  
 +
* Use ofLogical AND
 +
* Logical OR
 +
* Logical NOT
 +
* using a few examples
 
|-
 
|-
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide '''Prerequisites'''
+
|Display SlidePrerequisites
 
+
|To follow this tutorial you should have knowledge of''' '''
 
+
 
+
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| To follow this tutorial you should have knowledge of''' '''
+
  
 
* '''if-else statement, '''
 
* '''if-else statement, '''
* '''command line arguments '''and  
+
* '''command line arguments '''and
 
+
* 'quotingin BASH.'
# '''quoting '''in''' BASH.'''If not, for relevant tutorials please visit our website which is as shown.
+
 
+
 
+
  
 +
If not, for relevant tutorials, please visit our website, which is as shown.
 
|-
 
|-
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide  
+
|Display Slide
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| For this tutorial I am using  
+
|For this tutorial I am using
  
* '''Ubuntu Linux 12.04''' OS and
+
* Ubuntu Linux 12.04 OS
* '''GNU Bash''' version '''4.1.10'''
+
* GNU Bash version4.1.10
 
+
'''GNU Bash '''version '''4''' or above is recommended to practise this tutorial.
+
  
 +
'''GNU Bash '''version4 or above is recommended for practice.
 
|-
 
|-
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide  
+
|Display Slide
  
 
Logical Operators
 
Logical Operators
 +
|Let us understand the use of' Logical operators.'
  
 
+
* Logical operators are mainly used to control program flow
 
+
* Logical operators helps to link two' expressions' orconditions
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Let us understand the use of''' Logical operators.'''
+
* They can be a part of''' if, while,or some other control statements '''
 
+
* '''Logical operators'' '''''are mainly used to control program flow
+
* '''Logical operators''' helps to link two''' expressions''' or '''conditions'''
+
* They can be a part''' '''of''' if, a while, '''or''' '''some''' '''other''' control statements '''
+
 
+
 
+
 
+
 
|-
 
|-
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide
+
|Display Slide
  
 
Logical AND
 
Logical AND
Line 72: Line 54:
 
Syntax:
 
Syntax:
  
'''<nowiki>[ $condition1 ] && [ $condition2 ]</nowiki>'''
+
[ $condition1 ] &amp;&amp; [ $condition2 ]
 
+
 
+
'''<nowiki>[ $condition1 -a $condition2 ]</nowiki>'''
+
 
+
 
+
  
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Let's see the syntax of logical '''AND'''
+
[ $condition1 -a $condition2 ]
 +
|Let's see the syntax oflogical AND
  
* '''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
 
* Or we can use this syntax
 
* Or we can use this syntax
* '''Opening Square bracket''' space '''dollar symbol condition1 '''space '''hyphen a''' space '''dollar symbol condition2 '''space '''closing square bracket'''
+
* Opening square bracket space dollar
* '''Logical AND '''returns''' true '''when both''' condition1 '''and '''condition2''' are''' '''true
+
 
+
  
 +
symbol condition1 space hyphen a space dollar symbol condition2 space closing square bracket
  
 +
* '''Logical ANDreturns truewhen both condition1 '''andcondition2 aretrue
 
|-
 
|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"|  
+
|
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Let us see the syntax of '''Logical OR'''
+
|Let us see the syntax ofLogical OR
 
+
 
|-
 
|-
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide
+
|Display Slide
  
 
Logical OR
 
Logical OR
  
 +
'''[ $condition1 ]
 +
|[ $condition2 ]'''
  
'''<nowiki>[ $condition1 ] || [ $condition2 ]</nowiki>'''
+
[ $condition1 -o $condition2 ]
 
+
 
+
'''<nowiki>[ $condition1 -o $condition2 ]</nowiki>'''
+
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| * '''Opening Square bracket''' space '''dollar symbol condition1''' space '''closing square bracket '''space '''vertical bar vertical bar''' space '''Opening Square bracket''' space '''dollar symbol condition2''' space '''closing square bracket'''
+
* Or we can use this syntax
+
* '''Opening Square bracket''' space '''dollar symbol condition1 '''space '''hyphen o '''space''' dollar symbol condition2''' space '''closing square bracket'''
+
* '''Logical OR '''returns''' true '''when either''' condition1 '''or '''condition2 '''is '''true'''
+
 
+
 
+
 
+
 
|-
 
|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"|  
+
|
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Let us learn the usage of''' Logical OR''' and '''Logical AND''' using an example.
+
|Let us learn the usage of' Logical OR' andLogical AND using an example.
 
+
 
+
 
+
 
+
 
|-
 
|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Open file
+
|Open file
  
On T'''ermina'''l>> Type '''gedit logical.sh'''>> Press '''Enter'''
+
On Terminal&gt;&gt; Typegedit logical.sh&gt;&gt; PressEnter
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| I have already typed the code in a file named '''logical.sh'''.
+
|I have already typed the code in a file namedlogical.sh.
  
Open the terminal by pressing '''ctrl+alt+t''' keys simultaneousely on your keyboard.
+
Open theterminal by pressingctrl+alt+t keys simultaneousely on your keyboard.
  
 
Type:
 
Type:
  
'''gedit logical.sh &'''
+
gedit logical.sh &amp;
  
press''' Enter.'''
+
press' Enter.'
 
+
Now type the code as shown here in''' '''your''' logical.sh '''file.
+
  
 +
Now type the code as shown here in your''' logical.sh '''file.
 
|-
 
|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"|  
+
|
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Let me explain the code now.
+
|Let me explain the code now.
 
+
 
|-
 
|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| <nowiki>#!/bin/bash </nowiki>
+
|#!/bin/bash
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| This is the '''shebang line.'''
+
|This is theshebang line.
 
+
 
|-
 
|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| read -p "Enter a Word : " string  
+
|read -p &quot;Enter a Word : &quot; string
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| The''' read command''' reads''' one line''' of data from''' standard input.'''
+
|The' read command' reads one line of data from the' standard input.'
  
'''-p''' display the '''prompt.'''
+
- (hyphen) p display theprompt.
 
+
'''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.
 
|-
 
|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| <nowiki>if [ -z "$string" ]; then </nowiki>
+
|if [ -z &quot;$string&quot; ]; then
 
+
|Theif statement checks whether the entered string isempty.
 
+
 
+
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| The '''if statement''' checks whether the entered string is '''empty.'''
+
 
+
'''-z '''checks whether length of '''string''' is '''zero'''
+
  
 +
'''- (hyphen) z '''checks whether length ofstring iszero
 
|-
 
|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"|  
+
|
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Type '''man test '''on''' terminal '''to explore various other string comparisons.  
+
|Type '''man teston terminal '''to explore various otherstring comparisons.
 
+
 
|-
 
|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| echo "Nothing was entered "
+
|echo &quot;Nothing was entered &quot;
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| The '''echo''' '''statement '''will print a message if nothing was entered.
+
|Theecho '''statement '''will print a message if nothing was entered.
 
+
 
|-
 
|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''<nowiki>[Highlight]</nowiki>'''
+
|[Highlight]
  
<nowiki>elif [[ "$string" == *"raj"* ]] && [[ "$string" == *"jit"* ]]; then </nowiki>
+
elif [[ &quot;$string&quot; == *&quot;raj&quot;* ]] &amp;&amp; [[ &quot;$string&quot; == *&quot;jit&quot;* ]]; then
  
echo "$string contains both the words raj and jit"
+
echo &quot;$string contains both the words raj and jit&quot;
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| If the '''string''' is not empty, the program will move to the first '''elif statement.'''
+
|If thestring is not empty, the program will move to the firstelif statement.
  
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'andjit.
  
If yes, then it echoes out a message.  
+
If yes, then it echoes out a message.
  
Please note that '''logical AND''' is used here.
+
Please note thatlogical AND is used here.
 
+
Hence the message will be displayed only when both the conditions are satisfied.
+
  
 +
Hence, the message will be displayed only when both theconditions are satisfied.
 
|-
 
|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''<nowiki>[Highlight]</nowiki>'''
+
|[Highlight]
  
<nowiki>elif [[ "$string" == *"raj"* ]] || [[ $string = *"jit"* ]]; then </nowiki>
 
  
echo "$string contains word 'raj' or 'jit'"
 
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| If that is not so, then the program will move onto the second '''elif statement.'''
 
  
Here it checks whether the''' entered string''' contains either'' '''raj''''' or '''''jit.'''''
+
elif[[./"$string"%20==%20*"raj"*|&quot;$string&quot; == *&quot;raj&quot;*]]
 +
|[[./$string%20=%20*"jit"*|$string = *&quot;jit&quot;*]]; then
  
If yes, then it will display a message.
 
  
Please note that '''logical OR''' is used here.
 
 
The message will be displayed only when any one of the conditions are satisfied.
 
  
 +
echo &quot;$string contains word 'raj' or 'jit'&quot;
 
|-
 
|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| else  
+
|else
  
echo "Sorry! entered word '$string' does not contain either 'raj' or 'jit'"
+
echo &quot;Sorry! entered word '$string' does not contain either 'raj' or 'jit'&quot;
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Lastly, we have the default '''else statement.'''
+
|Lastly, we have the defaultelse statement.
  
 
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.
 
 
|-
 
|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| fi  
+
|fi
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''fi''' is the end of''' multilevel if-else''' loop.
+
|fi is the end of' multilevel if-else' loop.
  
 
Let us execute the program
 
Let us execute the program
 
 
|-
 
|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| On the '''terminal'''
+
|On theterminal
  
 +
&gt;&gt; Typechmod +x logical.sh&gt;&gt; PressEnter
  
>> Type '''chmod +x logical.sh'''>> Press '''Enter'''
+
&gt;&gt; Type./logical.sh&gt;&gt; PressEnter
 +
|Switch back to theterminal.
  
>> Type '''./logical.sh'''>> Press '''Enter'''
+
First make the file executable by typing-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Switch to the '''terminal.'''
+
  
First make the file executable by typing
+
'''chmod space plus x space logical dot sh '''
  
'''chmod''' space''' plus x''' space''' logical.sh '''
+
press' Enter'
 
+
Now type '''dot slash''' '''logical.sh '''and press''' Enter'''
+
  
 +
Now typedot slash'logical.shand press Enter'
 
|-
 
|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"|
+
|Highlight
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Let us give different inputs and see what happens.
+
  
|-
+
The output
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''Highlight'''
+
  
'''The output'''
+
Enter a Word:
 
+
 
+
'''Enter a Word:'''
+
  
 
Highlight
 
Highlight
Line 242: Line 184:
 
Type:
 
Type:
  
'''jitinraj'''
+
jitinraj
  
 +
jitinraj contains both the words raj and jit
 +
|The prompt displaysEnter a word:
  
'''jitinraj contains both the words raj and jit'''
+
I will enterjitinraj
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| The prompt displays '''Enter a word:'''
+
 
+
I will enter '''jitinraj'''
+
  
 
The output is:
 
The output is:
  
'''jitinraj contains both the words raj and jit'''
+
jitinraj contains both the words raj and jit
  
 
This means that the control was passed to the second statement.
 
This means that the control was passed to the second statement.
  
And as both the conditions are satisfied, it displays the message:
+
And as both theconditions are satisfied, it displays the message.
 
+
'''jitinraj contains both the words raj and jit'''
+
 
+
 
|-
 
|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Press '''up arrow key'''>> go to '''./logical.sh>>'''
+
|Pressup arrow key&gt;&gt; go to./logical.sh&gt;&gt;
  
Press '''Enter'''
+
PressEnter
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Now let us execute the script again.
+
|Now let us execute the script again.
  
 
Press the up '''arrow key. '''
 
Press the up '''arrow key. '''
  
Go to .'''/logical.sh '''and press '''Enter'''
+
Go to .'''/logical.sh '''and pressEnter
 
+
 
|-
 
|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Highlight
+
|Highlight
  
 
Type:
 
Type:
  
'''abhijit'''
+
abhijit
  
'''abijit contains word 'raj' or 'jit''''
+
abijit contains word 'raj' or 'jit'
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| The prompt displays '''Enter a word:'''
+
|The prompt displaysEnter a word:
  
This time I will enter '''abhijit.'''
+
This time I will enterabhijit.
  
And the output is:
+
The output is:
 
+
'''abhijit contains word 'raj' or 'jit'.'''
+
  
 +
abhijit contains word 'raj' or 'jit'.
 
|-
 
|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"|  
+
|
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Please try executing the program with different inputs and observe the output.
+
|Please try executing the program with different inputs and observe the output.
 
+
 
|-
 
|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"|  
+
|
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Let's switch back to our slides.  
+
|Let's switch back to our slides.
 
+
 
|-
 
|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide
+
|Display Slide
  
 
Logical NOT
 
Logical NOT
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Let's have a look at '''logical NOT '''operator.  
+
|Let's have a look at '''logical NOT '''operator.
 
+
* It inverts the '''boolean''' value of an expression.
+
* Which means, it returns '''true''' if the expression is '''false'''
+
* and returns '''false''' if the expression is '''true'''
+
 
+
 
+
  
 +
* It inverts theboolean value of an expression.
 +
* Which means, it returnstrue if the expression isfalse
 +
* and returnsfalse if the expression istrue
 
|-
 
|-
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide
+
|Display Slide
  
 
Logical NOT
 
Logical NOT
Line 313: Line 244:
 
Syntax
 
Syntax
  
! expression
+
[ ! expression ]
  
 +
[ ! expression ]
 +
|The syntax of '''logical NOT '''operator is
  
<nowiki>[ ! expression ]</nowiki>
+
* Exclamation mark spaceexpression
 
+
 
+
 
+
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| The syntax of '''logical NOT '''operator is
+
 
+
* '''Exclamation mark''' space '''expression'''
+
  
 
Or
 
Or
  
* '''Opening square bracket''' space '''exclamation mark''' space expression space '''closing square bracket'''
+
* Opening square bracket space exclamation mark space expression space closing square bracket
 
+
 
+
 
+
 
|-
 
|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"|  
+
|
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Let us see an example.
+
|Let us see an example.
 
+
 
|-
 
|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Open file
+
|Open file
  
On '''Terminal'''>> Type '''gedit logicalNOT.sh'''>> Press '''Enter'''
+
OnTerminal&gt;&gt; Typegedit logicalNOT.sh
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| I have already typed the code in a file.''' '''
+
  
So, I will go to the '''terminal '''and type '''gedit logicalNOT.sh '''
+
&gt;&gt; PressEnter
 +
|I have already typed the code in a file.
  
Press''' Enter.'''
+
So, I will go to the '''terminal '''and typegedit
  
|-
+
logicalNOT.sh space ampersand sign
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| <nowiki>#!/bin/bash</nowiki>
+
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| This is the''' shebang line, '''as we already know.
+
  
 +
Press' Enter.'
 +
|-
 +
|
 +
|Now type the code as shown here in yourlogicalNOT.sh file.
 
|-
 
|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''<nowiki>[Highlight]</nowiki>'''
+
|#!/bin/bash
 +
|This is the''' shebang line, '''as we already know.
 +
|-
 +
|[Highlight]
  
<nowiki>if [ ! -f "$1" ]; then</nowiki>
+
if [ ! -f &quot;$1&quot; ]; then
 +
|$1 is the first''' command line argument '''passed to the script.
  
 
+
'''- (hyphen) f '''checks if the file exists with the same name that was passed as anargument.
 
+
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''$1''' is the first''' command line argument '''passed to the script.
+
 
+
 
+
'''-f '''checks if the file exists with the same name that was passed as an '''argument'''.
+
  
 
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.
 
 
|-
 
|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Point to the NOT operator with cursor.
+
|Point to the NOT operator with cursor.
 +
|ThisNOT operator here inverses the returned value.
  
 +
Which means, if a file of that name exists, the conditon will betrue.
  
 
+
But the '''NOT operator '''will inverse its value tofalse.
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| This '''NOT operator''' here inverses the returned value.
+
 
+
Which means, if a file of that name exists, the conditon will be '''true.'''
+
 
+
But the '''NOT operator '''will inverse its value to '''false'''.  
+
 
+
 
|-
 
|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''echo "File $1 does not exist"'''
+
|echo &quot;File $1 does not exist&quot;
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| And it will display the message  
+
|And it will display the message
 
+
'''FILE does not exist'''
+
  
 +
FILE does not exist
 
|-
 
|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| else
+
|else
  
echo "File $1 exist"
+
echo &quot;File $1 exist&quot;
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| And here in the '''else statement, '''it displays the message  
+
|And here in the '''else statement, '''it displays the message
 
+
'''FILE exists'''
+
  
 +
FILE exists
 
|-
 
|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| fi
+
|fi
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| '''fi''' marks the end of '''if loop.'''
+
|fi marks the end ofif loop.
 
+
 
|-
 
|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| On the '''terminal'''
+
|On theterminal
 
+
'''touch test.txt'''
+
 
+
 
+
  
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Switch to the '''terminal'''
+
touch test.txt
 +
|Switch to theterminal. Let me clear the prompt.
  
Let's create an empty file with the name '''test.txt.'''
+
Let's create an empty file with the nametest.txt
  
 
So, type :
 
So, type :
  
'''touch space test.txt'''
+
touch space test dot txt
 
+
 
|-
 
|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| >> Type '''chmod +x logicalNOT.sh'''>> Press '''Enter'''
+
|&gt;&gt; Typechmod +x logicalNOT.sh&gt;&gt; PressEnter
  
>> Type '''./logicalNOT.sh test.txt'''>> Press '''Enter'''
+
&gt;&gt; Type./logicalNOT.sh test.txt&gt;&gt; PressEnter
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Next, make the script executable by typing:''' '''
+
|Next, make the script executable by typing:''' '''
  
'''chmod''' space''' plus x''' space''' logicalNOT.sh '''
+
chmod space plus x space logicalNOT dot sh
 
+
Now type '''dot slash''' '''logical.sh space test.txt '''and press''' Enter.'''
+
  
 +
Now type'dot slash logical.sh space test.txtand press Enter.'
 
|-
 
|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Point to test.txt in the previous command  
+
|Point to test.txt in the previous command
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Our shell script will check whether the file exists.
+
|Our shell script will check whether the file exists.
  
Our file'' '''''test.txt '''exists'''''<nowiki>;</nowiki>''''' hence the value will be''' true.'''
+
Our file'test.txtexists ; hence the value will be' true.'
  
Then the '''logical NOT''' will inverse that''' '''value and return '''false.'''
+
Then thelogical NOT will inverse that value and returnfalse.
 
+
Because the''' '''evaluation is '''false''', the '''else '''statement is evaluated.
+
  
 +
Because the evaluation isfalse, theelse statement is evaluated.
 
|-
 
|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Show Output
+
|Show Output
  
'''File 'test.txt' exists'''
+
File 'test.txt' exists
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| And the message displayed is -
+
|And the message displayed is -
 
+
'''File 'test.txt' exists'''
+
  
 +
File 'test.txt' exists
 
|-
 
|-
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"|  
+
|
| style="border-top:none;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Try executing the program again with argument '''test1.txt'''
+
|Try executing the program again with argumenttest1.txt
  
And observe the control flow as explained before.
 
  
 +
 +
And observe the control flow, as explained before.
 
|-
 
|-
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide  
+
|Display Slide
  
 
Summary
 
Summary
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Let us summarize.
+
|Come back to our slides. Let us summarize.
  
In this tutorial we learnt the usage of,  
+
In this tutorial we learnt the usage of,
  
* '''logical AND'''
+
* logical AND
 
* '''logical OR '''and
 
* '''logical OR '''and
* '''logical NOT operators'''
+
* logical NOT
 
+
 
+
 
+
 
|-
 
|-
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide  
+
|Display Slide
  
 
Assignment
 
Assignment
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Check whether  
+
|Check whether
  
* a file exists and is executable  
+
* a file exists and is executable
 
* using the '''logical operators '''
 
* using the '''logical operators '''
 
* explained in this tutorial
 
* explained in this tutorial
* (Hint: '''man test''')
+
* (Hint:man test)
 
+
 
+
 
+
 
|-
 
|-
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide  
+
|Display Slide
 +
|Watch the video available at the link shown below
  
 
+
It summarizes the Spoken Tutorial project
 
+
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| 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
 
If you do not have good bandwidth, you can download and watch it
 
 
|-
 
|-
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide  
+
|Display Slide
 
+
  
 
Spoken Tutorial Workshops
 
Spoken Tutorial Workshops
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| The Spoken Tutorial Project Team  
+
|The Spoken Tutorial Project Team
  
Conducts workshops using spoken tutorials  
+
Conducts workshops using spoken tutorials
  
Gives certificates to those who pass an online test  
+
Gives certificates to those who pass an online test
  
 
For more details, please write to
 
For more details, please write to
  
 
contact@spoken-tutorial.org
 
contact@spoken-tutorial.org
 
 
|-
 
|-
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide  
+
|Display Slide
  
 
Acknowledgement
 
Acknowledgement
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| 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
  
 
It is supported by the National Mission on Education through ICT, MHRD, Government of India
 
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
+
More information on this Mission is available at:[http://spoken-tutorial.org/NMEICT-Intro http://spoken-tutorial.org/NMEICT-Intro]
 
+
 
|-
 
|-
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| Display Slide  
+
|Display Slide
| style="border:1pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.191cm;padding-right:0.191cm;"| The script has been contributed by FOSSEE and spoken-tutorial team
+
|The script has been contributed by FOSSEE and spoken-tutorial team
  
 
This is Ashwini from IIT Bombay.
 
This is Ashwini from IIT Bombay.
  
 
Thank you for joining.
 
Thank you for joining.
 
 
|}
 
|}

Latest revision as of 12:45, 25 November 2014

Title of script: Logical Operators in Bash

Author: Lavitha pereira

Keywords: Video tutorial, Bash Shell, Logical AND, Logical OR, Logical NOT

Visual Cue
Narration
Display Slide Dear friends, Welcome to the Spoken tutorial on

Logical Operators in Bash

Display Slide In this tutorial, we will learn
  • Use ofLogical AND
  • Logical OR
  • Logical NOT
  • using a few examples
Display SlidePrerequisites To follow this tutorial you should have knowledge of
  • if-else statement,
  • command line arguments and
  • 'quotingin BASH.'

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

Display Slide For this tutorial I am using
  • Ubuntu Linux 12.04 OS
  • GNU Bash version4.1.10

GNU Bash version4 or above is recommended for practice.

Display Slide

Logical Operators

Let us understand the use of' Logical operators.'
  • Logical operators are mainly used to control program flow
  • Logical operators helps to link two' expressions' orconditions
  • They can be a part of if, while,or some other control statements
Display Slide

Logical AND

Syntax:

[ $condition1 ] && [ $condition2 ]

[ $condition1 -a $condition2 ]

Let's see the syntax oflogical AND
  • 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
  • Or we can use this syntax
  • Opening square bracket space dollar

symbol condition1 space hyphen a space dollar symbol condition2 space closing square bracket

  • Logical ANDreturns truewhen both condition1 andcondition2 aretrue
Let us see the syntax ofLogical OR
Display Slide

Logical OR

[ $condition1 ]

[ $condition2 ]

[ $condition1 -o $condition2 ]

Let us learn the usage of' Logical OR' andLogical AND using an example.
Open file

On Terminal>> Typegedit logical.sh>> PressEnter

I have already typed the code in a file namedlogical.sh.

Open theterminal by pressingctrl+alt+t keys simultaneousely on your keyboard.

Type:

gedit logical.sh &

press' Enter.'

Now type the code as shown here in your logical.sh file.

Let me explain the code now.
#!/bin/bash This is theshebang line.
read -p "Enter a Word : " string The' read command' reads one line of data from the' standard input.'

- (hyphen) p display theprompt.

string is a' variable' which stores the text entered by the user, during execution.

if [ -z "$string" ]; then Theif statement checks whether the entered string isempty.

- (hyphen) z checks whether length ofstring iszero

Type man teston terminal to explore various otherstring comparisons.
echo "Nothing was entered " Theecho statement will print a message if nothing was entered.
[Highlight]

elif "$string" == *"raj"* && "$string" == *"jit"* ; then

echo "$string contains both the words raj and jit"

If thestring is not empty, the program will move to the firstelif statement.

Here it checks whether the entered' string' contains both the words'raj'andjit.

If yes, then it echoes out a message.

Please note thatlogical AND is used here.

Hence, the message will be displayed only when both theconditions are satisfied.

[Highlight]


elif[[./"$string"%20==%20*"raj"*|"$string" == *"raj"*]]

[[./$string%20=%20*"jit"*|$string = *"jit"*]]; then


echo "$string contains word 'raj' or 'jit'"

else

echo "Sorry! entered word '$string' does not contain either 'raj' or 'jit'"

Lastly, we have the defaultelse statement.

When all the above statements are false, then this statement will be executed.

fi fi is the end of' multilevel if-else' loop.

Let us execute the program

On theterminal

>> Typechmod +x logical.sh>> PressEnter

>> Type./logical.sh>> PressEnter

Switch back to theterminal.

First make the file executable by typing-

chmod space plus x space logical dot sh

press' Enter'

Now typedot slash'logical.shand press Enter'

Highlight

The output

Enter a Word:

Highlight

Type:

jitinraj

jitinraj contains both the words raj and jit

The prompt displaysEnter a word:

I will enterjitinraj

The output is:

jitinraj contains both the words raj and jit

This means that the control was passed to the second statement.

And as both theconditions are satisfied, it displays the message.

Pressup arrow key>> go to./logical.sh>>

PressEnter

Now let us execute the script again.

Press the up arrow key.

Go to ./logical.sh and pressEnter

Highlight

Type:

abhijit

abijit contains word 'raj' or 'jit'

The prompt displaysEnter a word:

This time I will enterabhijit.

The output is:

abhijit contains word 'raj' or 'jit'.

Please try executing the program with different inputs and observe the output.
Let's switch back to our slides.
Display Slide

Logical NOT

Let's have a look at logical NOT operator.
  • It inverts theboolean value of an expression.
  • Which means, it returnstrue if the expression isfalse
  • and returnsfalse if the expression istrue
Display Slide

Logical NOT

Syntax

[ ! expression ]

[ ! expression ]

The syntax of logical NOT operator is
  • Exclamation mark spaceexpression

Or

  • Opening square bracket space exclamation mark space expression space closing square bracket
Let us see an example.
Open file

OnTerminal>> Typegedit logicalNOT.sh

>> PressEnter

I have already typed the code in a file.

So, I will go to the terminal and typegedit

logicalNOT.sh space ampersand sign

Press' Enter.'

Now type the code as shown here in yourlogicalNOT.sh file.
#!/bin/bash This is the shebang line, as we already know.
[Highlight]

if [ ! -f "$1" ]; then

$1 is the first command line argument passed to the script.

- (hyphen) f checks if the file exists with the same name that was passed as anargument.

So, it will return true if the file exists and false if it does not exist.

Point to the NOT operator with cursor. ThisNOT operator here inverses the returned value.

Which means, if a file of that name exists, the conditon will betrue.

But the NOT operator will inverse its value tofalse.

echo "File $1 does not exist" And it will display the message

FILE does not exist

else

echo "File $1 exist"

And here in the else statement, it displays the message

FILE exists

fi fi marks the end ofif loop.
On theterminal

touch test.txt

Switch to theterminal. Let me clear the prompt.

Let's create an empty file with the nametest.txt

So, type :

touch space test dot txt

>> Typechmod +x logicalNOT.sh>> PressEnter

>> Type./logicalNOT.sh test.txt>> PressEnter

Next, make the script executable by typing:

chmod space plus x space logicalNOT dot sh

Now type'dot slash logical.sh space test.txtand press Enter.'

Point to test.txt in the previous command Our shell script will check whether the file exists.

Our file'test.txtexists ; hence the value will be' true.'

Then thelogical NOT will inverse that value and returnfalse.

Because the evaluation isfalse, theelse statement is evaluated.

Show Output

File 'test.txt' exists

And the message displayed is -

File 'test.txt' exists

Try executing the program again with argumenttest1.txt


And observe the control flow, as explained before.

Display Slide

Summary

Come back to our slides. Let us summarize.

In this tutorial we learnt the usage of,

  • logical AND
  • logical OR and
  • logical NOT
Display Slide

Assignment

Check whether
  • a file exists and is executable
  • using the logical operators
  • explained in this tutorial
  • (Hint:man test)
Display Slide 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

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

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 The script has been contributed by FOSSEE and spoken-tutorial team

This is Ashwini from IIT Bombay.

Thank you for joining.

Contributors and Content Editors

Ashwini, Nancyvarkey