Difference between revisions of "PERL/C2/Comments-in-Perl/English"

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| style="border:0.5pt solid #000000;padding:0.106cm;"| Slide:Learning Objectives
 
| style="border:0.5pt solid #000000;padding:0.106cm;"| Slide:Learning Objectives
−
| style="border:0.5pt solid #000000;padding:0.106cm;"| In this tutorial, we will learn about
+
| style="border:0.5pt solid #000000;padding:0.106cm;"| In this tutorial, we will learn about comments in '''Perl'''.
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+
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Comments in '''Perl'''
+
  
 
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|-
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You can use any text editor of your choice.
 
You can use any text editor of your choice.
  
 +
|-
 +
| style="border-top:none;border-bottom:0.5pt solid #000000;border-left:0.5pt solid #000000;border-right:0.5pt solid #000000;padding:0.106cm;"| Slide:System Requirements
 +
| style="border-top:none;border-bottom:0.5pt solid #000000;border-left:0.5pt solid #000000;border-right:0.5pt solid #000000;padding:0.106cm;"| You should have basic knowledge of compiling, executing and '''Variables''' in '''Perl'''.
  
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You should have Basic knowledge of Compiling, Executing and Variables in Perl
+
If not, please go through the relevant spoken tutorials on the spoken tutorial website.
−
 
+
−
If not, please go through the relevant spoken tutorials on the spoken tutorial website  
+
  
 
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| style="border-top:none;border-bottom:0.5pt solid #000000;border-left:0.5pt solid #000000;border-right:0.5pt solid #000000;padding:0.106cm;"| Here is a demo.
 
| style="border-top:none;border-bottom:0.5pt solid #000000;border-left:0.5pt solid #000000;border-right:0.5pt solid #000000;padding:0.106cm;"| Here is a demo.
  
−
Let us open a new file in the Text Editor.
+
Let us open a new file in the '''Text Editor'''.
  
 
|-
 
|-
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'''gedit comments dot pl &'''
 
'''gedit comments dot pl &'''
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−
 
−
 
  
 
|-
 
|-
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'''hash Declaring count variable'''
 
'''hash Declaring count variable'''
  
−
'''press enter'''
+
press '''enter'''
  
 
'''dollar count space equal to space 1 semicolon'''
 
'''dollar count space equal to space 1 semicolon'''
  
−
'''press enter'''
+
press '''enter'''
  
 
'''print space double quotes Count is dollar count slash n double quote complete semicolon space hash prints Count is 1'''
 
'''print space double quotes Count is dollar count slash n double quote complete semicolon space hash prints Count is 1'''
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|-
 
|-
 
| style="border-top:none;border-bottom:0.5pt solid #000000;border-left:0.5pt solid #000000;border-right:0.5pt solid #000000;padding:0.106cm;"| Save the file.
 
| style="border-top:none;border-bottom:0.5pt solid #000000;border-left:0.5pt solid #000000;border-right:0.5pt solid #000000;padding:0.106cm;"| Save the file.
−
| style="border-top:none;border-bottom:0.5pt solid #000000;border-left:0.5pt solid #000000;border-right:0.5pt solid #000000;padding:0.106cm;"| Now Save this file by pressing ctlr s file and execute the '''Perl''' script.
+
| style="border-top:none;border-bottom:0.5pt solid #000000;border-left:0.5pt solid #000000;border-right:0.5pt solid #000000;padding:0.106cm;"| Now save this file by pressing '''Ctlr S''' and execute the '''Perl''' script.
  
 
|-
 
|-
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This tells us that there is no syntax error
 
This tells us that there is no syntax error
−
 
−
 
−
 
  
 
|-
 
|-
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| style="border-top:none;border-bottom:0.5pt solid #000000;border-left:0.5pt solid #000000;border-right:0.5pt solid #000000;padding:0.106cm;"| Let us switch back to '''gedit'''.
 
| style="border-top:none;border-bottom:0.5pt solid #000000;border-left:0.5pt solid #000000;border-right:0.5pt solid #000000;padding:0.106cm;"| Let us switch back to '''gedit'''.
  
−
in '''gedit''', go to the first line and press enter.
+
in '''gedit''', go to the first line and press '''enter'''.
  
 
Go back to the first line and type the following command.
 
Go back to the first line and type the following command.
  
 
'''Hash exclamation mark slash usr slash bin slash perl'''
 
'''Hash exclamation mark slash usr slash bin slash perl'''
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−
 
−
 
  
 
|-
 
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|-
 
|-
 
| style="border-top:none;border-bottom:0.5pt solid #000000;border-left:0.5pt solid #000000;border-right:0.5pt solid #000000;padding:0.106cm;"| Slide
 
| style="border-top:none;border-bottom:0.5pt solid #000000;border-left:0.5pt solid #000000;border-right:0.5pt solid #000000;padding:0.106cm;"| Slide
−
| style="border-top:none;border-bottom:0.5pt solid #000000;border-left:0.5pt solid #000000;border-right:0.5pt solid #000000;padding:0.106cm;"| '''Note:''' Though this line starts with hash''' '''symbol, it will not be considered as a single line comment by '''Perl'''.
+
| style="border-top:none;border-bottom:0.5pt solid #000000;border-left:0.5pt solid #000000;border-right:0.5pt solid #000000;padding:0.106cm;"| '''Note:''' Though this line starts with hash''' '''symbol, it will not be considered as a '''single line comment''' by '''Perl'''.
  
−
Now let us look at multiline comments
+
Now let us look at '''multiline comments'''.
  
 
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|-
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| style="border:0.5pt solid #000000;padding:0.106cm;"| '''Multi Line'''
 
| style="border:0.5pt solid #000000;padding:0.106cm;"| '''Multi Line'''
  
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This type of comment is used  
+
This type of '''comment''' is used  
  
 
* when user wants to comment a piece of code or  
 
* when user wants to comment a piece of code or  
 
* to add description/usage of piece of code
 
* to add description/usage of piece of code
  
−
This type of comment starts with the symbol '''equal to''' '''''head''''' and ends with '''equal to ''cut'''''
+
This type of '''comment''' starts with the symbol '''equal to ''head''''' and ends with '''equal to ''cut'''''
  
 
|-
 
|-
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| style="border-top:none;border-bottom:0.5pt solid #000000;border-left:0.5pt solid #000000;border-right:0.5pt solid #000000;padding:0.106cm;"| Lets switch back to '''gedit''' and type the following -
 
| style="border-top:none;border-bottom:0.5pt solid #000000;border-left:0.5pt solid #000000;border-right:0.5pt solid #000000;padding:0.106cm;"| Lets switch back to '''gedit''' and type the following -
  
−
in the '''comments dot pl '''file
+
in the '''comments dot pl '''file, at the end of file, type
−
 
+
−
at the end of file type
+
  
 
'''equal to head'''
 
'''equal to head'''
  
−
'''press enter'''
+
press '''enter'''
  
 
'''print space double quote count variable will be used for counting purpose double quote complete'''
 
'''print space double quote count variable will be used for counting purpose double quote complete'''
  
−
'''press enter'''
+
press '''enter'''
  
 
'''equal to cut'''
 
'''equal to cut'''
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and press '''Enter'''
 
and press '''Enter'''
−
| style="border-top:none;border-bottom:0.5pt solid #000000;border-left:0.5pt solid #000000;border-right:0.5pt solid #000000;padding:0.106cm;"| so let us execute it
+
| style="border-top:none;border-bottom:0.5pt solid #000000;border-left:0.5pt solid #000000;border-right:0.5pt solid #000000;padding:0.106cm;"| So let us execute it
  
 
'''perl comments dot pl'''
 
'''perl comments dot pl'''
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|-
 
|-
 
| style="border-top:none;border-bottom:0.5pt solid #000000;border-left:0.5pt solid #000000;border-right:0.5pt solid #000000;padding:0.106cm;"|  
 
| style="border-top:none;border-bottom:0.5pt solid #000000;border-left:0.5pt solid #000000;border-right:0.5pt solid #000000;padding:0.106cm;"|  
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| style="border-top:none;border-bottom:0.5pt solid #000000;border-left:0.5pt solid #000000;border-right:0.5pt solid #000000;padding:0.106cm;"| '''Please note''' there should not be any leading or trailing space(s) before '''<nowiki>= to</nowiki>''' sign and after the '''head''', '''cut''', '''begin''' or '''end''' word.
+
| style="border-top:none;border-bottom:0.5pt solid #000000;border-left:0.5pt solid #000000;border-right:0.5pt solid #000000;padding:0.106cm;"| '''Please note''' there should not be any leading or trailing space(s) before '''<nowiki>= to</nowiki>''' sign and after the '''head, cut, begin''' or '''end''' word.
  
 
|-
 
|-
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'''print “Addition is $addition”;'''
 
'''print “Addition is $addition”;'''
 
| style="border-top:none;border-bottom:0.5pt solid #000000;border-left:0.5pt solid #000000;border-right:0.5pt solid #000000;padding:0.106cm;"| Type the following commands as shown on the screen.
 
| style="border-top:none;border-bottom:0.5pt solid #000000;border-left:0.5pt solid #000000;border-right:0.5pt solid #000000;padding:0.106cm;"| Type the following commands as shown on the screen.
 +
 +
 +
 +
 +
  
 
Here I am declaring two variables '''firstNum '''and '''secondNum '''and I am assigning some values to them.
 
Here I am declaring two variables '''firstNum '''and '''secondNum '''and I am assigning some values to them.
 +
 +
  
 
Then I have commented this portion here.
 
Then I have commented this portion here.
  
−
Now I added these two numbers and assign the value to a third variable named addition.
 
  
−
Next I want to print the value using print command.
 
  
  
  
 +
 +
 +
Now I added these two numbers and assigned the value to a third '''variable''' named '''addition'''.
 +
 +
 +
 +
Next I want to print the value using '''print command'''.
  
 
|-
 
|-
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−
On terminal type
+
On '''terminal''' type
  
 
'''perl hyphen c commentsExample dot pl'''
 
'''perl hyphen c commentsExample dot pl'''
  
−
press enter
+
press '''enter'''
  
−
There is no syntax error
+
There is no syntax error.
  
−
so execute the script by typing
+
So execute the script by typing
  
  
 
'''perl commentsExample dot pl'''
 
'''perl commentsExample dot pl'''
  
−
press enter
+
press '''enter'''
  
 
|-
 
|-
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* Single Line Comment.  
 
* Single Line Comment.  
 
* Mutli Line Comment.  
 
* Mutli Line Comment.  
−
 
−
 
  
 
|-
 
|-
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It summarises the Spoken Tutorial project  
 
It summarises the Spoken Tutorial project  
  
−
If you do not have good bandwidth, you can  
+
If you do not have good bandwidth, you can download and watch it  
−
 
+
−
download and watch it  
+
  
 
|-
 
|-
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| style="border:0.5pt solid #000000;padding:0.106cm;"| The Spoken Tutorial Project Team  
 
| style="border:0.5pt solid #000000;padding:0.106cm;"| The Spoken Tutorial Project Team  
  
−
Conducts workshops using spoken tutorials  
+
*Conducts workshops using spoken tutorials  
  
−
Gives certificates to those who pass an online  
+
*Gives certificates to those who pass an online test
  
−
test
+
For more details, please write to contact at spoken hyphen tutorial dot org  
−
 
+
−
For more details, please write to  
+
−
 
+
−
contact at spoken hyphen tutorial dot org  
+
  
 
|-
 
|-
 
| style="border:0.5pt solid #000000;padding:0.106cm;"| Acknowledgment
 
| style="border:0.5pt solid #000000;padding:0.106cm;"| Acknowledgment
−
| style="border:0.5pt solid #000000;padding:0.106cm;"| Spoken Tutorial Project is a part of the Talk to a  
+
| style="border:0.5pt solid #000000;padding:0.106cm;"| Spoken Tutorial Project is a part of the Talk to a Teacher project.
−
 
+
−
Teacher project  
+
−
 
+
−
It is supported by the National Mission on
+
−
 
+
−
Education through ICT, MHRD, Government
+
−
 
+
−
of India
+
  
−
More information on this Mission is available
+
It is supported by the National Mission on Education through ICT, MHRD, Government of India.
  
−
at the following link.
+
More information on this Mission is available at the following link.
  
 
|-
 
|-

Latest revision as of 09:43, 27 June 2018

Title of script: Comments in Perl

Author: Amol

Keywords: Comments in Perl, Video Tutorials, Scalars in Perl


Visual Cue
Narration
Slide Welcome to the spoken tutorial on Comments in Perl.
Slide:Learning Objectives In this tutorial, we will learn about comments in Perl.
Slide:System Requirements I am using Ubuntu Linux12.04 operating system and

Perl 5.14.2

that is, Perl revision 5 version 14 and subversion 2


I will also be using the gedit Text Editor.

You can use any text editor of your choice.

Slide:System Requirements You should have basic knowledge of compiling, executing and Variables in Perl.

If not, please go through the relevant spoken tutorials on the spoken tutorial website.

Slide Commenting a piece of code in Perl can be done in two ways:

a. Single Line

b. Multi Line

Slide Single Line

This type of comment is used

  • when user wants to comment a single line of code or
  • to add one liner text to explain the functionality of a piece of code

This type of comment starts with the symbol # (hash).

Here is a demo.

Let us open a new file in the Text Editor.

Switch to the Terminal and type

gedit singlemulti.pl &

and press Enter.

Open the Terminal and type -

gedit comments dot pl &

Highlight & Once again, reminding you that the ampersand is used to free the command prompt in the terminal. And press enter
Type

# Declaring count variable

$count = 1;

print “Count is $count \n”; # prints Count is 1

Now type the following commands.

hash Declaring count variable

press enter

dollar count space equal to space 1 semicolon

press enter

print space double quotes Count is dollar count slash n double quote complete semicolon space hash prints Count is 1

Save the file. Now save this file by pressing Ctlr S and execute the Perl script.
Switch to the Terminal and type

perl -c singlemulti.pl

and press Enter

Switch to the Terminal, and type

perl hyphen c comments dot pl

and press Enter.

This tells us that there is no syntax error

Then type

perl singlemulti.pl

and press Enter

Now type

perl comments dot pl

and press Enter.

Point to the output It will show the following output -

Count is 1

Go to gedit and type

#!/usr/bin/perl


Let us switch back to gedit.

in gedit, go to the first line and press enter.

Go back to the first line and type the following command.

Hash exclamation mark slash usr slash bin slash perl

Slide This line in Perl is called as a shebang line and is the first line in a Perl program.

It tells where to find the Perl Interpreter.

Slide Note: Though this line starts with hash symbol, it will not be considered as a single line comment by Perl.

Now let us look at multiline comments.

Slide Multi Line

This type of comment is used

  • when user wants to comment a piece of code or
  • to add description/usage of piece of code

This type of comment starts with the symbol equal to head and ends with equal to cut

Type

=head

print “ count variable will be used for counting purpose”

=cut

above

$count = 1;

Lets switch back to gedit and type the following -

in the comments dot pl file, at the end of file, type

equal to head

press enter

print space double quote count variable will be used for counting purpose double quote complete

press enter

equal to cut

Save the file and close it. Save the file, close it and execute the Perl script.
Switch to the Terminal and type

perl -c singlemulti.pl

and press Enter.

On the Terminal, type

perl hyphen c comments dot pl

and press Enter.

No syntax error

Then type

perl singlemulti.pl

and press Enter

So let us execute it

perl comments dot pl

Point to the output It will show the same output as before.

Count is 1

Switch back to gedit

Point to the sentence

“count variable will be used for counting purpose”

It does not print the sentence “count variable is be used for counting purpose”
Point to =head and =cut This is because we commented the portion using equal to head and equal to cut
Slide You can either use =head =cut or =begin =end.

These are not the special keywords used by Perl.

Please note there should not be any leading or trailing space(s) before = to sign and after the head, cut, begin or end word.
Switch to the Terminal Open the Terminal once again.
Type

perl gedit comments.pl &

and press Enter.

And Type -

gedit commentsExample dot pl &

and press Enter.

Type

# Here I am going to explain commenting in Perl

# Following is the scalar variable declaration

$firstNum = 10;

$secondNum = 20;


=head

following piece of code adds 2 numbers

puts the result into a 3rd variable

and prints this 3rd variable

=cut

$addition = $firstNum + $secondNum;

print “Addition is $addition”;

Type the following commands as shown on the screen.




Here I am declaring two variables firstNum and secondNum and I am assigning some values to them.


Then I have commented this portion here.




Now I added these two numbers and assigned the value to a third variable named addition.


Next I want to print the value using print command.

Save the file and switch to the Terminal.

Type

perl -c comments.pl

perl comments.pl

Save the file and execute the Perl script on the Terminal.


On terminal type

perl hyphen c commentsExample dot pl

press enter

There is no syntax error.

So execute the script by typing


perl commentsExample dot pl

press enter

Point to the output It will show the following output.

Addition is 30

Summary This brings us to the end of this tutorial.

Here we learnt,

To Add Comments in Perl

Assignment Assignment
  1. Write a perl script to find square of a number.
  2. Explain the functionality of the code written using:
  • Single Line Comment.
  • Mutli Line Comment.
About the Project Watch the video available at the following link

It summarises the Spoken Tutorial project

If you do not have good bandwidth, you can download and watch it

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 at spoken hyphen tutorial dot org

Acknowledgment 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 the following link.

Hope you enjoyed this Perl tutorial.

This is Amol Brahmankar signing off.

Thanks for joining.

Contributors and Content Editors

AmolBrahmankar, Nancyvarkey, Sneha

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