PERL/C2/Comments-in-Perl/English
Title of script: Comments in Perl
Author: Amol
Keywords: Comments in Perl, Video Tutorials, Scalars in Perl
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| 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
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
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
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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
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;
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.
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.
perl hyphen c commentsExample dot pl press enter There is no syntax error. So execute the script by typing
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
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| 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
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. |
