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Time Narration
00:00 Welcome to the spoken tutorial on Comments in Perl.
00:05 In this tutorial, we will learn about
00:08 comments in Perl.
00:10 I am using Ubuntu Linux 12.04 operating system and Perl 5.14.2
00:18 that is, Perl revision 5 version 14 and subversion 2.
00:23 I will also be using the gedit Text Editor.
00:27 You can use any text editor of your choice.
00:31 You should have basic knowledge of compiling, executing and variables in Perl.
00:37 If not, please go through the relevant spoken tutorials on the spoken tutorial website.
00:43 Commenting a piece of code in Perl can be done in two ways:
00:47 Single Line , Multi-Line.
00:49 This type of comment is used when user wants to comment a single line of code or
00:55 to add one liner text to explain the functionality of a piece of code.
01:01 This type of comment starts with the symbol # (hash).
01:05 Here is a demo. Let us open a new file in the Text Editor.
01:11 Open the Terminal and type - gedit comments dot pl space &
01:19 Once again reminding you that the ampersand is used to free the command prompt in the terminal, now press Enter.
01:27 Now type the following commands.
01:29 hash Declaring count variable press Enter.
01:37 dollar count space equal to space 1 semicolon press Enter.
01:45 print space double quotes Count is dollar count slash n double quotes complete semicolon space hash Prints Count is 1
02:03 Now save this file by pressing Ctrl S and execute the Perl script.
02:08 Switch to the Terminal and type perl hyphen c comments dot pl and press Enter.
02:18 This tells us that there is no syntax error.
02:21 Now type: perl comments dot pl and press Enter.
02:28 It will show the following output - Count is 1
02:33 Let us switch back to gedit.
02:36 In gedit, go to the first line and press Enter.
02:40 Go back to the first line and type the following command.
02:44 Hash exclamation mark slash usr slash bin slash perl
02:52 This line in Perl is called as shebang line and is the first line in a Perl program.
02:59 It tells where to find the Perl Interpreter.
03:03 Note: Though this line starts with hash symbol, it will not be considered as a single line comment by Perl.
03:11 Now let us look at multiline comments.
03:13 Multi Line: This type of comment is used
03:17 when user wants to comment a piece of code or to add description/usage of piece of code.
03:25 This type of comment starts with the symbol equal to head and ends with equal to cut.
03:33 Let's switch back to gedit and type the following in the comments dot pl file.
03:39 At the end of file, type: equal to head, press Enter.
03:45 print space double quote count variable is used for counting purpose double quote complete press Enter.
03:59 equal to cut
04:01 Save the file, close it and execute the Perl script.
04:05 On the Terminal, type: perl hyphen c comments dot pl and press Enter.
04:13 No syntax error.
04:15 So let us execute it, perl comments dot pl
04:21 It will show the same output as before. Count is 1.
04:27 It does not print the sentence “count variable is used for counting purpose”.
04:32 This is because we commented the portion using equal to head and equal to cut.
04:40 You can either use =head =cut or =begin =end.
04:48 These are not the special keywords used by Perl.
04:52 Please note, there should not be any leading or trailing space(s) before '=' (equal to sign) and after the head, cut, begin or end word.
05:02 Open the Terminal once again.
05:05 And Type - gedit commentsExample dot pl space & and press Enter.
05:15 Type the following commands as shown on the screen.
05:19 Here, I am declaring two variables firstNum and secondNum and I am assigning some values to them.
05:28 Then I have commented this portion here.
05:32 Now I added these two numbers and assign the value to a third variable named addition.
05:39 Next, I want to print the value using print command.
05:44 Save the file and execute the Perl script on the Terminal.
05:49 On terminal, type: perl hyphen c commentsExample dot pl, press Enter.
05:57 There is no syntax error.
05:59 So, execute the script by typing
06:01 perl commentsExample dot pl press Enter.
06:07 It will show the following output. Addition is 30.
06:12 This brings us to the end of this tutorial.
06:16 Here, we learnt to add comments in Perl.
06:19 Write a perl script to find square of a number.
06:23 Explain the functionality of the code written using single line comment & multiline Comment.
06:30 Watch the video available at the following link.
06:34 It summarizes the Spoken Tutorial project.
06:37 If you do not have good bandwidth, you can download and watch it.
06:42 The Spoken Tutorial Project Team:
06:44 Conducts workshops using spoken tutorials.
06:48 Gives certificates to those who pass an online test.
06:51 For more details, please write to contact at spoken hyphen tutorial dot org.
06:58 Spoken Tutorial Project is a part of the Talk to a Teacher project.
07:03 It is supported by the National Mission on Education through ICT, MHRD, Government of India.
07:11 More information on this mission is available at the following link.
07:15 Hope you enjoyed this Perl tutorial. This is Amol Brahmankar, signing off.

Thanks for joining.

Contributors and Content Editors

Gaurav, Madhurig, PoojaMoolya, Sandhya.np14, Sneha