Difference between revisions of "PERL/C3/Access-Modifiers-in-PERL/English-timed"
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|You can declare a '''variable''' without giving it a value, like this: | |You can declare a '''variable''' without giving it a value, like this: | ||
| − | '''my $fvalue<nowiki>semicolon</nowiki>''' | + | '''my $fvalue<nowiki> semicolon </nowiki>''' |
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| − | |'''my $fname = within double quotes Rahul semicolon''' | + | |'''my $fname''' = within double quotes '''Rahul semicolon''' |
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| 02:02 | | 02:02 | ||
| − | |'''my''' open bracket '''$fname comma $lname comma $age''' close bracket '''semicolon''' | + | |'''my''' open bracket '''$fname''' comma '''$lname''' comma '''$age''' close bracket '''semicolon''' |
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|05:17 | |05:17 | ||
| − | |Open the '''terminal''' and type '''gedit scope | + | |Open the '''terminal''' and type '''gedit scope hyphen local dot pl ampersand''' and press '''Enter'''. |
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|06:31 | |06:31 | ||
| − | |Switch back to the '''terminal''' and type, '''perl scope | + | |Switch back to the '''terminal''' and type, '''perl scope hyphen local.pl''' and press '''Enter'''. |
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| 09:21 | | 09:21 | ||
| − | |The '''package variable''' is referred by '''package name | + | |The '''package variable''' is referred by '''package name colon colon variable name''' |
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| − | |''local''' '''$age = 52''' semicolon | + | |'''local''' '''$age = 52''' semicolon |
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Revision as of 10:42, 26 November 2015
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| 00:01 | Welcome to the Spoken Tutorial on Access Modifiers in PERL |
| 00:07 | In this tutorial we will learn about
|
| 00:19 | For this tutorial, I am using
|
| 00:32 | You can use any text editor of your choice. |
| 00:36 | You should have basic knowledge of Perl Programming. |
| 00:40 | If not, then go through the relevant Perl spoken tutorials on the spoken tutorial website. |
| 00:47 | Let us start with the introduction to the Scope of variables. |
| 00:51 | The scope of a variable is the region of code within which a variable can be accessed. |
| 00:58 | In other words, it refers to the visibility of variables. |
| 01:03 | First, we will discuss about my, local and our modifiers in Perl. |
| 01:10 | my means Private variables |
| 01:13 | local means Dynamically scoped variables |
| 01:17 | our means Global variables |
| 01:20 | Variables declared with my keyword will lose scope outside the block in which they are declared. |
| 01:28 | You can declare a variable without giving it a value, like this:
my $fvalue semicolon |
| 01:37 | You can also declare a variable by assigning a value to it, as: |
| 01:43 | my $fValue = 1 semicolon |
| 01:48 | my $fname = within double quotes Rahul semicolon |
| 01:55 | The syntax to declare several variables with the same my statement is as follows: |
| 02:02 | my open bracket $fname comma $lname comma $age close bracket semicolon |
| 02:12 | Let us understand private variables using a sample program. |
| 02:17 | I already have a sample program. Let me open it in gedit Text editor. |
| 02:24 | Open the terminal and type gedit scope hyphen my dot pl ampersand and press Enter |
| 02:34 | Scope-my dot pl file is now open in gedit. |
| 02:39 | Type the following code as displayed on the screen. Let me explain the code now. |
| 02:46 | Here, I have declared a private variable $fname with my keyword. |
| 02:52 | And assigned the value "Raghu" to it. |
| 02:56 | Within this block, the print statement prints the value in the fname variable, i.e. "Raghu". |
| 03:04 | In the next block, I have assigned the value "Other" to the same private variable $fname. |
| 03:11 | So, the print statement will print "Other" within this particular block. |
| 03:17 | The last print statement in this program, will not print any output. |
| 03:23 | This is because outside the scope of the blocks defined earlier, fname has no value assigned to it. |
| 03:32 | Now, press Ctrl+S to save the file. |
| 03:37 | Let us now execute the program. |
| 03:40 | Switch back to the terminal and type perl scope hyphen my dot pl and press Enter. |
| 03:49 | The output is displayed as Block 1: Raghu
Block 2: Other Outside Block: There is no output |
| 03:59 | So, the scope of the my variable is accessed only within a particular block of code. |
| 04:06 | Now let us change the existing program a little. |
| 04:10 | Let us add my $fname = within double quotes John semicolon outside the blocks, before the last print statement.
Save the changes |
| 04:23 | Switch back to the terminal and execute as before. |
| 04:28 | Analyse the output that is displayed. |
| 04:32 | Hope you are able to understand the scope of using my variable within a block and outside a block. |
| 04:41 | Next we will see about dynamically scoped variable in Perl. |
| 04:47 | Local keyword gives a temporary scope to a global variable. |
| 04:52 | The variable is visible to any function called from the original block. |
| 04:58 | You can declare a local variable as,
local $fValue = 100 semicolon local $fname” = within double quotes Rakesh semicolon |
| 05:13 | Let us understand this using a sample program. |
| 05:17 | Open the terminal and type gedit scope hyphen local dot pl ampersand and press Enter. |
| 05:27 | This will open scope hyphen local dot pl file in gedit. |
| 05:33 | Type the following code as displayed on the screen. Let me explain the code now. |
| 05:40 | Here, in the first line we have declared a variable $fname and initialised it. |
| 05:47 | Inside the function Welcome, we have declared a local variable by the same name, $fname. |
| 05:54 | Notice the local keyword before the variable name. |
| 05:59 | And we have assigned the value "Rakesh" to this variable. |
| 06:03 | So, basically, inside function Welcome(), $fname is modified as a new temporary local variable.
Then, the function Hello is being called. |
| 06:15 | Here is the function definition of Hello. |
| 06:18 | At the end of the program, we are calling both the functions Welcome and Hello. |
| 06:25 | Now press Ctrl + S to save the program. |
| 06:29 | Let us execute the program. |
| 06:31 | Switch back to the terminal and type, perl scope hyphen local.pl and press Enter. |
| 06:41 | The output is displayed as Hello, Rakesh ! Hello, Welcome to Spoken tutorials! |
| 06:48 | Let us understand the output. |
| 06:51 | When the function Welcome() is called, the function Hello() within it, accesses the local variable. |
| 06:59 | Within Welcome(), $fname has the value "Rakesh". |
| 07:04 | After this, the function Hello() accesses the variable $fname once again. |
| 07:11 | But this time, it is the variable $fname which was initialized to "Welcome to spoken tutorials". |
| 07:19 | It does not access the local variable $fname within the function Welcome(). |
| 07:25 | Which means that, the local variable restores the scope, after leaving the block Welcome(). |
| 07:32 | Next, we will see about global variables in Perl. |
| 07:38 | A global variable can be accessed anywhere in the program. |
| 07:43 | Global variables are declared with our keyword. |
| 07:47 | Here are some examples. our $fvalue = 100 semicolon </nowiki> our $fname =within double quotes Priya semicolon |
| 08:01 | Now let us look at a working example of global variables. |
| 08:06 | Switch back to the terminal and type gedit scope hyphen our dot pl ampersand and press Enter |
| 08:16 | This will open the file scope hyphen our.pl in gedit. |
| 08:22 | Let me explain the sample program which I have written. |
| 08:27 | I have declared package main and a global variable as our $i and I have initialised it to 100 |
| 08:37 | Notice the package First declaration. |
| 08:40 | A package is a collection of code, which has its own namespace. |
| 08:46 | Namespace prevents variable name collisions between packages. |
| 08:51 | We will see more about package and namespace in future tutorials. |
| 08:56 | Within package First, the global variable "i" holds the value 10. |
| 09:02 | In package Second, the global variable "i" is assigned the value 20. |
| 09:08 | The main package uses both package First variable and the package Second variable. |
| 09:15 | In my program, I have declared the same variable "i" in all the packages. |
| 09:21 | The package variable is referred by package name colon colon variable name |
| 09:29 | In our example it is $First colon colon i, $Second colon colon i |
| 09:39 | We have multiple packages within one file, and the global variable will be accessed by all the packages. |
| 09:47 | Now, save the file and execute the program. |
| 09:51 | So, switch to terminal and type perl scope hyphen our dot pl and press Enter. |
| 09:59 | The output is as displayed on the terminal. |
| 10:03 | Analyze the output by yourself to understand how the assignment to the variable i was done. |
| 10:11 | This brings us to the end of this tutorial. Let us summarise. |
| 10:16 | In this tutorial, we learnt:
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| 10:29 | It is preferred to use my than local as the compilation is faster. |
| 10:35 | Here is an assignment for you. |
| 10:37 | Write the code for the following assignment and execute it. |
| 10:42 | Declare a package as FirstModule |
| 10:46 | Declare a variable $age as our and assign the value 42 |
| 10:52 | Declare another package as SecondModule |
| 10:56 | Declare a variable $ageword as our and assign the value within double quotes "Forty-Two" |
| 11:05 | Declare a subroutine First() |
| 11:08 | Inside the subroutine, declare two variables with local and my keyword as below: |
| 11:16 | local $age = 52 semicolon |
| 11:20 | my $ageword = within double quotes Fifty-two semicolon |
| 11:27 | Call another subroutine as Result() |
| 11:31 | Print the values of $age and $ageword inside this function. |
| 11:37 | End the subroutine |
| 11:39 | Declare the subroutine Result() |
| 11:42 | Again print the values of $age and $ageword |
| 11:47 | End the subroutine |
| 11:49 | Call the function First() |
| 11:51 | Print the Package First and Package Second as below: |
| 11:57 | The video at the following link summarises the Spoken Tutorial project.
Please download and watch it. |
| 12:05 | The Spoken Tutorial Project Team conducts workshops and gives certificates for those who pass an online test.
For more details, please write to us. |
| 12:18 | Spoken Tutorial project is funded by NMEICT, MHRD, Government of India.
More information on this mission is available at this link. |
| 12:31 | This is Nirmala Venkat from IIT Bombay, signing off. Thanks for watching. |
