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 Linux12.04 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 condition 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 condition close bracket space open curly bracket |
| 01:30 | Press Enter |
| 01:31 | 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 |
| 01:45 | code semicolon to be executed when both the above conditions are false semicolon |
| 01:51 | Press Enter |
| 01:52 | close curly bracket |
| 01:55 | First, the if condition is checked and executed if the condition 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 variable language. |
| 02:44 | Note that, eq is string comparison operator. |
| 02:49 | And then we have the various conditons 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 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. |
| 04:19 | The output shown on terminal is |
| 04:22 | I am not a computer language |
| 04:27 | The 3 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 execute. |
| 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 or 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
|
| 06:10 | else space open curly bracket executes when dollar value does not match any of the cases |
| 06:18 | Close curly bracket |
| 06:19 | 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'll 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 3 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 a 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 |
| 10:05 | using sample programs. |
| 10:08 | Watch the video available at the following link
|
| 10:12 | It summaries 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. |
