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

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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 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 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 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. The value is to 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 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 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 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 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 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
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11:51 This is Nirmala Venkat from IIT Bombay, signing off. Thanks for watching.

Contributors and Content Editors

PoojaMoolya, Sandhya.np14