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 dot 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 are 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 are 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	Re-usability of code is implemented through modules.
03:30	These are similar to libraries in other (computer) 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 dot 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 dot 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 dot 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 dot 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	1: (one) is to find the square of a number.
08:20	2: Two is for square root of a number.
08:23	3: Three is for a random number in the given range. 4: Four is to quit the program.
08:29	If option 1 (one) is typed, it will ask the user to enter a number.
08:34	The value is stored in $number. The value is passed to the function square() in commonfunctions dot 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 2 (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 3 (three) is typed, a random number is displayed as output in the given range.
09:09	Else, if option is 4 (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 dot 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 summarize.
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 dot pm using ‘use’ method.
10:50	Write the below functions in Letter dot pm file.
10:54	LetterDate() function returns the current date and time.
10:58	To() function returns the names of the participants.
11:02	From() function returns the sender's name.
11:05	Lettermsg() function returns the contents 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 summarizes 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.
11:36	For more details, please write to us.
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