PERL/C2/More-Conditional-statements/English-timed

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 .
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 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 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.
04:19	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 .
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 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
10:05	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.

Contributors and Content Editors

Gaurav, PoojaMoolya, Sandhya.np14