PERL/C3/Including-files-or-modules/English-timed

Time	Narration
00:01	Welcome to the Spoken Tutorial on Including files or modules in a PERL program
00:08	In this tutorial we will learn to use do use and require methods in PERL programming.
00:16	For this tutorial, I am using Ubuntu Linux 12.04 operating system Perl 5.14.2 and gedit Text Editor
00:28	You can use any text editor of your choice.
00:32	To follow this tutorial, you should have working knowledge of Perl programming.
00:37	If not, then go through the relevant Perl spoken tutorials on the spoken tutorial website.
00:44	Do Method: These are simple ways to include the source code from other files into the current script file.
00:53	Let us understand how to use do() method.
00:57	Open a new file in your text editor and name it as datetime.pl
01:03	In the datetime dot pl file, type the following code as displayed on the screen.
01:09	From here onwards, remember to press the Enter key after every command on the terminal.
01:15	Let us understand the code now.
01:18	The current date and time is stored in a variable dollar datestring.
01:23	Here, I have a function by name msgThanks, which returns a “Thank you” message.
01:31	Now, press Ctrl+S to save the file.
01:35	Next let us look at another Perl program which will make use of this file datetime dot pl
01:43	Open a new file in your text editor and name it as main dot pl
01:49	In the main dot pl file, type the following code as displayed on the screen.
01:55	Let me explain the code now.
01:58	Here, the first line prints the welcome message.
02:03	do() method is called with the filename from where we want to use the code.
02:09	Current date and time is stored in the $datestring variable of datetime dot pl file.
02:16	And at the end, we call the msgThanks() function from the same file.
02:21	Now, press Ctrl+S to save the file.
02:25	Let us execute the program.
02:27	Switch back to the terminal and type perl main dot pl and press Enter
02:34	Observe the output on the terminal.
02:37	Next we will learn how to use require method and use method in a Perl program.
02:44	These methods are used - when we have collections of subroutines that can be used in multiple Perl programs.
02:52	use method is used only for the modules.
02:56	It is verified at the time of compilation
02:59	There is no need to give the file extension
03:03	require method is used for both Perl programs and modules
03:08	It is verified at the run time
03:10	One needs to give the file extension.
03:14	The syntax of use method is use module name semicolon
03:20	Perl modules are the files which end with .pm extension.
03:25	Reusability of code is implemented through modules.
03:30	These are similar to libraries in other languages.
03:35	Now I will show a simple program with the use method to include a module in Perl code.
03:43	Open a new file In your text editor and name it as sum dot pm.
03:49	In the sum dot pm file, type the following code as displayed on the screen.
03:55	Here, I have a simple function which will calculate the sum of a given set of numbers.
04:01	Now, press Ctrl+S to save the file
04:05	We will write another Perl script where we’ll use this sum.pm file.
04:11	Let me open the sample program app dot pl file which I have saved already
04:17	In the app dot pl file, type the following code as displayed on the screen.
04:22	Let me explain the code now.
04:25	The first line shows the use method with the module name.
04:29	In our case, the module name is sum.
04:33	We are passing 1,7,5,4,9 as input parameters to the function total in sum dot pm file.
04:44	Again, in the next line, we are passing 1 to 10 as input parameters to the same function.
04:52	Now, press Ctrl+S to save the file.
04:56	Let us execute the program.
04:59	Switch back to the terminal and type perl app dot pl and Press Enter
05:06	Observe the output displayed on the terminal.
05:10	Let us see few more options in use method. Switch back to sum.pm in the text editor.
05:18	At the beginning of the source code, add the lines use strict semicolon use warnings semicolon
05:27	use strict and use warnings are compiler flags that instruct Perl to behave in a stricter way.
05:35	These are used to avoid common programming mistakes.
05:39	use strict forces the user to declare all the variables used in the program.
05:45	If there are errors, use strict will abort the execution.
05:50	use warnings will only provide warnings but continue with the execution.
05:56	Assume that we forgot to declare the variable $sum as my.
06:02	Let us now see how the same program is executed.
06:06	Press Ctrl+S to save the file.
06:09	Switch back to the terminal and type perl app dot pl
06:15	We can see that the program is aborted without executing the result.
06:21	The first set of lines displayed on the terminal are error messages generated by “use strict”.
06:29	The last two are the abort messages.
06:32	So, this is how the use method options work.
06:36	Next let us see a Perl program where we use the require method.
06:41	Let me open the sample program commonfunctions.pl which I have already saved.
06:48	Type the following code as displayed on the screen in your commonfunctions dot pl file. Let us understand the code now.
06:57	Here we can see a collection of commonly used functions.
07:01	The first function square() returns the square of a number.
07:06	The second function square underscore root() returns the square root of a given number.
07:12	Next function random underscore number() generates a random number.
07:18	The last function random underscore range() generates a random number between a lower range and upper range of numbers.
07:26	Note that we need the 1 semicolon at the end of the file.
07:31	This is because Perl needs the last expression in the file to return a true value.
07:37	Now, press Ctrl+S to save the file.
07:41	Next we will write a Perl program in which we’ll call these subroutines using require method.
07:48	Let me open the sample program callprogram dot pl which I have already saved.
07:54	Type the following code as displayed on the screen in your file. Let me explain the code now.
08:02	require reads the commonfunctions.pl file containing Perl code and compiles it.
08:09	This program gives 4 options to the user. The user has to choose one option at a time.
08:17	One is to find the square of a number.
08:20	Two is for square root of a number.
08:23	Three is for a random number in the given range. Four is to quit the program.
08:29	If option one is typed, it will ask the user to enter a number.
08:34	The value is stored in $number. This is passed to the function square in commonfunctions.pl file.
08:44	The function returns the square of a number.
08:47'	The print statement prints the square of a number as output.
08:52	If option two is typed, the square root of a number is displayed as output.
08:58	The execution is followed as explained in the previous function square.
09:03	If option three is typed, a random number is displayed as output in the given range.
09:09	Else if option is four, the program exits. If any option other than the ones specified is given, the print statement says “Incorrect option”.
09:20	Note that in this program we have called only three functions out of four from commonfunctions.pl.
09:28	Now, press Ctrl+S to save the file
09:31	Let us execute the program.
09:34	Switch back to the terminal and type perl callprogram dot pl
09:41	Observe the output
09:44	I'll execute the program once again with a different option.
09:49	Type perl callprogram dot pl
09:53	Now, Enter the Option as 3.
09:56	Enter a lower range as 50.
09:59	Enter a upper range as 99.
10:02	We can see the random number is generated in the given range of numbers.
10:08	Try other options on your own.
10:11	This brings us to the end of this tutorial. Let us summarise.
10:16	In this tutorial we learnt to use do use require methods in PERL programming.
10:24	Note: "use Module" is recommended over "require Module", because it determines module availability at compile time.
10:33	Here is an assignment for you. Write a Perl program reminder.pl where you will write a letter to the participants.
10:41	Prompt the user to enter To and From name
10:45	Call the subroutines from Letter.pm using ‘use’ method.
10:50	Write the below functions in Letter.pm file.
10:54	LetterDate() function returns the current date and time
10:58	To() function returns the name of the participants
11:02	From() function returns the sender name
11:05	Lettermsg() function returns the content of the letter
11:09	Thanksmsg() function returns thanks and regards.
11:13	The output should be displayed as shown here.
11:20	The video at the following link summarize the spoken tutotial project. Please download and watch it
11:27	The Spoken Tutorial Project Team conducts workshops using spoken tutorials and gives certificates on passing online tests.
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11:40	Spoken Tutorial project is funded by NMEICT, MHRD, Government of India. More information on this mission is available at this link.
11:51	This is Nirmala Venkat from IIT Bombay, signing off. Thanks for watching.

Contributors and Content Editors

PoojaMoolya, Sandhya.np14