PERL/C2/More-Conditional-statements/English-timed
From Script | Spoken-Tutorial
| Time | Narration |
| 00:00 | Welcome to the spoken tutorial on if-elsif-else and switch conditional statements in PERL. |
| 00:07 | In this tutorial, we will learn about |
| 00:10 | the if-elsif-else statement and switch statement in Perl . |
| 00:15 | I am using Ubuntu Linux 12.04 operating system and Perl 5.14.2. |
| 00:22 | I will also be using the gedit Text Editor. |
| 00:25 | You can use any text editor of your choice. |
| 00:29 | You should have basic knowledge of variables and comments in Perl |
| 00:34 | and knowledge of for, foreach, while and do-while loops and |
| 00:38 | if and if-else statements will be an added advantage. |
| 00:43 | Please go through the relevant spoken tutorials on the Spoken Tutorial website. |
| 00:48 | If-elsif-else statement in Perl can be used |
| 00:52 | to test multiple conditions and |
| 00:54 | when all conditions fail then it executes the default else block. |
| 00:59 | The syntax of if-elsif-else statement is as follows. |
| 01:04 | if space open bracket condition1 close bracket space open curly bracket press Enter |
| 01:13 | piece of code to be executed when the condition is true semicolon |
| 01:18 | press Enter . |
| 01:20 | Close curly bracket space elsif space open bracket condition2 close bracket space open curly bracket |
| 01:30 | press Enter , another piece of code semicolon |
| 01:33 | to be executed when elsif condition is true |
| 01:37 | press Enter . |
| 01:39 | Close curly bracket space else space open curly bracket |
| 01:44 | Enter. Code to be executed when both the above conditions are false semicolon |
| 01:51 | press Enter .Close curly bracket. |
| 01:55 | First, the if condition is checked and executed if the condition1 is true. |
| 02:01 | If not, then the else if condition is checked and executed if it is true. |
| 02:06 | Otherwise, the code within else block is executed. |
| 02:11 | Now let us look at an example of if-elsif-else statement. |
| 02:16 | Open the Terminal and type: |
| 02:19 | gedit conditionalBlocks dot pl space ampersand |
| 02:26 | and press Enter. |
| 02:28 | This will open the " conditionalBlocks.pl" file in gedit. |
| 02:33 | Type the following piece of code as displayed on the screen. |
| 02:38 | We have assigned the value 'Perl' to the variable language. |
| 02:44 | Note that eq is string comparison operator. |
| 02:49 | And then we have various conditions that we want to check. |
| 02:55 | Now, press Ctrl+s to save the file. |
| 02:58 | Then switch to terminal and execute file directly. |
| 03:02 | Type: perl conditionalBlocks dot pl |
| 03:09 | Note: I am skipping the compilation step. It is not a mandatory step for executing Perl scripts. |
| 03:16 | If there is any compilation error, |
| 03:18 | execution will throw an error and will stop execution of script. |
| 03:23 | Now press Enter. |
| 03:25 | The output shown on the terminal is |
| 03:27 | "Hi, I am Perl" |
| 03:29 | Now, let us look at our next case. |
| 03:31 | Switch to gedit. |
| 03:33 | Assign 'Java' to variable language as shown. |
| 03:37 | Press Ctrl+s to save the file. |
| 03:40 | Switch to the terminal and execute the file. |
| 03:43 | Type: perl conditionalBlocks dot pl |
| 03:50 | and press Enter. |
| 03:53 | The output shown on the terminal is "Hi, I am Java". |
| 03:59 | Again let us switch back to gedit. |
| 04:03 | Now, let us assign 'English' to the language variable. |
| 04:07 | Press ctrl+s to save the file. |
| 04:09 | Switch to the terminal and execute the file. |
| 04:13 | Type: perl conditionalBlocks dot pl |
| 04:18 | and press Enter. The output shown on the terminal is: |
| 04:22 | "I am not a computer language". |
| 04:27 | The three cases imply that |
| 04:29 | only one if block that satisfies the condition will be executed. |
| 04:35 | Otherwise the default else block will get executed. |
| 04:39 | We can have multiple elsif conditions as per our requirement, like this. |
| 04:46 | Here is an assignment for you - |
| 04:48 | Write an if-elsif-else statement to print |
| 04:51 | “I am a Science graduate” if stream is 'science' |
| 04:55 | “I am a Commerce graduate” if stream is 'commerce' |
| 04:59 | “I am an Arts graduate” if stream is neither 'science' nor 'commerce'. |
| 05:06 | Now let us learn about the switch statement. |
| 05:10 | Till Perl 5.8, there was no switch statement in Perl. |
| 05:14 | After that, Switch module was introduced |
| 05:18 | which provided the functionality of switch statement. |
| 05:22 | Note: Modules in Perl will be covered in subsequent tutorials. |
| 05:27 | The syntax of switch is as follows: |
| 05:30 | use Switch semicolon |
| 05:32 | press Enter |
| 05:34 | switch space open bracket $ (dollar) value close bracket space open curly bracket |
| 05:42 | press Enter |
| 05:44 | case space 1 space open curly bracket executes when dollar value equal to 1 close curly bracket. |
| 05:53 | Press Enter. |
| 05:55 | case space single quote a single quote space open curly bracket executes when dollar value equal to single quote a single quote close curly bracket |
| 06:09 | Press Enter . else space open curly bracket executes when dollar value does not match any of the cases |
| 06:18 | close curly bracket. Press Enter . |
| 06:20 | Close curly bracket. |
| 06:22 | Let us understand switch using a sample program. |
| 06:26 | Open the Terminal and type: |
| 06:29 | gedit sampleSwitch dot pl space ampersand |
| 06:36 | and press Enter. |
| 06:38 | Now, type the sample program as shown on the screen. |
| 06:43 | Let us understand how the switch statement works. |
| 06:46 | The use Switch statement includes the Switch module inside the Perl code. |
| 06:54 | Note: We will learn about use keyword, in detail, in subsequent tutorials. |
| 07:00 | Now we will test the different cases. |
| 07:03 | We have assigned 'Perl' to the variable $var. |
| 07:08 | The value in variable $var is checked in the switch statement. |
| 07:14 | In the first case, it matches with the case 'Perl'. |
| 07:19 | So, the code written against this case will be executed. |
| 07:24 | Press ctrl+s to save the file. |
| 07:27 | Now, switch to terminal and execute the script |
| 07:31 | perl sampleSwitch.pl |
| 07:36 | press Enter. |
| 07:38 | The following output is shown on the terminal |
| 07:41 | "I am Perl" |
| 07:43 | Switch back to sampleSwitch.pl in gedit. |
| 07:48 | Now, let us assign 'Linux' to the variable $var. |
| 07:52 | Press Ctrl+S to save the file. |
| 07:57 | Again, the value of variable $var will be checked in switch. |
| 08:03 | It matches with the case 'Linux'. |
| 08:05 | So, code written against this case will get executed. |
| 08:10 | Now, switch to terminal and execute the script. |
| 08:15 | perl sampleSwitch.pl |
| 08:19 | press Enter. |
| 08:21 | The following output is shown on the terminal. |
| 08:24 | "I am Linux" |
| 08:26 | Switch to sampleSwitch.pl in gedit. |
| 08:30 | Similarly, if variable $var has value 'Java' then second case will be checked. |
| 08:38 | Now, let us assign 'English' to the variable $var. |
| 08:42 | Again, the value of variable $var will be checked in switch. |
| 08:47 | It does not match any of the case statements. |
| 08:50 | So, the else statement will be executed. |
| 08:54 | Now, switch to terminal and execute the script. |
| 09:00 | perl sampleSwitch.pl |
| 09:07 | and press Enter. |
| 09:09 | The following output is shown on the terminal: |
| 09:12 | "I am not a computer language" |
| 09:17 | The three cases imply that: |
| 09:20 | The value of the expression decides the case to be executed. |
| 09:25 | Only the valid case will be executed and |
| 09:28 | when there is no valid case then the default else case will be executed. |
| 09:35 | It is not mandatory to write the else case. |
| 09:39 | In such scenario, |
| 09:41 | if none of the cases match |
| 09:44 | then there will be no output from the switch statement. |
| 09:48 | Here is another assignment for you: |
| 09:50 | Re-write the previous assignment |
| 09:53 | given earlier, in this tutorial, using switch statement. |
| 09:57 | Let us summarize. |
| 09:59 | In this tutorial, we have learnt: |
| 10:01 | if-elsif-else statement and |
| 10:04 | switch statement in Perl using sample programs. |
| 10:08 | Watch the video available at the following link. |
| 10:12 | It summarizes the Spoken Tutorial project. |
| 10:15 | If you do not have good bandwidth, you can download and watch it. |
| 10:20 | The Spoken Tutorial project team: Conducts workshops using spoken tutorials. |
| 10:25 | Gives certificates to those who pass an online test. |
| 10:30 | For more details, please write to: contact at spoken hyphen tutorial dot org. |
| 10:36 | "Spoken Tutorial" project is a part of the "Talk to a Teacher" project. |
| 10:40 | It is supported by the National Mission on Education through ICT, MHRD, Government of India. |
| 10:47 | More information on this mission is available at: spoken hyphen tutorial dot org slash NMEICT hyphen Intro. |
| 10:58 | Hope you enjoyed this PERL tutorial. |
| 11:00 | This is Amol, signing off. |
| 11:03 | Thanks for joining. |
