Difference between revisions of "PERL/C3/Access-Modifiers-in-PERL/English-timed"

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|-
 
|-
 
|00:01
 
|00:01
−
|Welcome to the''' Spoken Tutorial''' on''' Access Modifiers in PERL'''
+
|Welcome to the''' Spoken Tutorial''' on''' Access Modifiers in PERL'''.
  
 
|-
 
|-
 
|00:07
 
|00:07
−
|In this tutorial we will learn about
+
|In this tutorial, we will learn about:
−
 
+
Scope of variables
−
* Scope of variables
+
'''Private''' variables
−
* Private variables
+
'''Dynamically scoped''' variables
−
* Dynamically scoped variables
+
'''Global''' variables
−
* Global variables
+
  
 
|-
 
|-
 
|00:19
 
|00:19
−
|For this tutorial, I am using
+
|For this tutorial, I am using:
−
 
+
'''Ubuntu Linux 12.04''' operating system
−
* '''Ubuntu Linux 12.04''' operating system
+
'''Perl 5.14.2''' and the
−
* '''Perl 5.14.2'''
+
'''gedit''' Text Editor.
−
* and the''' gedit''' Text Editor
+
  
 
|-
 
|-
 
|00:32
 
|00:32
−
|You can use any text editor of your choice.
+
|You can use any '''text editor''' of your choice.
  
 
|-
 
|-
 
|00:36
 
|00:36
−
|You should have basic knowledge of '''Perl''' Programming.
+
|You should have basic knowledge of '''Perl''' programming.
  
 
|-
 
|-
Line 39: Line 37:
 
|-
 
|-
 
|00:47
 
|00:47
−
|Let us start with the introduction to the''' Scope of variables'''.
+
|Let us start with the introduction to the scope of variables .
  
 
|-
 
|-
Line 53: Line 51:
 
|First, we will discuss about''' my, local''' and''' our''' modifiers in '''Perl.'''
 
|First, we will discuss about''' my, local''' and''' our''' modifiers in '''Perl.'''
  
−
* '''my '''means '''Private variables'''
+
|-
−
* '''local''' means '''Dynamically scoped variables'''
+
|01:10
−
* '''our '''means '''Global variables'''
+
| '''my '''means '''Private variables''',
 +
 
 +
|-
 +
|01:13
 +
| '''local''' means '''Dynamically scoped variables''',
 +
 
 +
|-
 +
|01:17
 +
| '''our '''means '''Global variables'''.
  
 
|-
 
|-
 
|01:20
 
|01:20
−
|'''Variables '''declared with''' my''' keyword will lose scope outside the '''block''' in which they are declared.
+
|Variables declared with''' my''' keyword will lose scope outside the '''block''' in which they are declared.
  
 
|-
 
|-
 
|01:28
 
|01:28
−
|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>'''
  
 
|-
 
|-
 
|01:37
 
|01:37
−
|You can also declare a '''variable''' by assigning a value to it, as:
+
|You can also declare a variable by assigning a value to it, as:
  
 
|-
 
|-
Line 76: Line 82:
 
|-
 
|-
 
| 01:48
 
| 01:48
−
|'''my $fname =  within double quotes Rahul semicolon'''
+
|'''my $fname''' =  within double quotes '''Rahul semicolon'''
  
 
|-
 
|-
 
| 01:55
 
| 01:55
−
|The syntax to declare several '''variables '''with the same''' my''' statement is as follows:  
+
|The syntax to declare several variables with the same''' my''' statement is as follows:  
  
 
|-
 
|-
 
| 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
  
 
|-
 
|-
 
|02:12
 
|02:12
−
|Let us understand '''private variables''' using a sample program.
+
|Let us understand '''private''' variables using a sample program.
  
 
|-
 
|-
 
|02:17
 
|02:17
−
|I already have a sample program. Let me open it in '''gedit Text editor'''.
+
|I already have a sample program. Let me open it in ''''gedit' Text editor'''.
  
 
|-
 
|-
 
|02:24
 
|02:24
−
|Open the '''terminal '''and type''' gedit scope hyphen my dot pl ampersand '''and press '''Enter'''
+
|Open the '''terminal '''and type:''' gedit scope hyphen my dot pl ampersand '''and press '''Enter'''.
  
 
|-
 
|-
Line 108: Line 114:
 
|-
 
|-
 
|02:46
 
|02:46
−
|Here, I have declared a '''private variable $fname''' with''' my''' keyword.
+
|Here, I have declared a '''private''' variable '''$fname''' with 'my' keyword
  
 
|-
 
|-
 
| 02:52
 
| 02:52
−
|And assigned the value "'''Raghu'''" to it.
+
|and assigned the value "Raghu" to it.
  
 
|-
 
|-
 
|02:56
 
|02:56
−
|Within this block, the '''print statement''' prints the value in the '''fname variable''', i.e. "'''Raghu'''".
+
|Within this block, the '''print''' statement prints the value in the '''fname''' variable i.e. "Raghu".
  
 
|-
 
|-
 
|03:04
 
|03:04
−
|In the next block, I have assigned the value "'''Other'''" to the same '''private variable $fname.'''
+
|In the next block, I have assigned the value "Other" to the same '''private''' variable '''$fname.'''
  
 
|-
 
|-
 
|03:11
 
|03:11
−
|So, the '''print statement '''will print "'''Other'''" within this particular block.
+
|So, the '''print statement '''will print "Other", within this particular block.
  
 
|-
 
|-
 
|03:17
 
|03:17
−
|The last '''print statement '''in this program, will not print any output.  
+
|The last '''print statement '''in this program will not print any output.  
  
 
|-
 
|-
 
|03:23
 
|03:23
−
|This is because outside the scope of the blocks defined earlier, '''fname '''has no value assigned to it.
+
|This is because, outside the scope of the blocks defined earlier, '''fname '''has no value assigned to it.
  
 
|-
 
|-
Line 144: Line 150:
 
|-
 
|-
 
|03:40
 
|03:40
−
|Switch back to the '''terminal '''and type '''perl scope hyphen my dot pl '''and press '''Enter'''.
+
|Switch back to the '''terminal '''and type: '''perl scope hyphen my dot pl '''and press '''Enter'''.
  
 
|-
 
|-
 
|03:49
 
|03:49
−
|The output is displayed as '''Block 1: Raghu'''
+
|The output is displayed as:
−
 
+
"Block 1: Raghu"
−
'''Block 2: Other'''
+
"Block 2: Other"
−
 
+
"Outside Block: " there is no output.
−
'''Outside Block: ''' There is no output
+
  
 
|-
 
|-
 
| 03:59
 
| 03:59
−
|So, the scope of the '''my variable '''is accessed only within a particular block of code.
+
|So, the scope of the ''''my' variable '''is accessed only within a particular block of code.
  
 
|-
 
|-
 
|04:06
 
|04:06
−
|Now let us change the existing program a little.
+
|Now, let us change the existing program a little.
  
 
|-
 
|-
 
| 04:10
 
| 04:10
−
|Let us add ''' my $fname = "John" semicolon''' outside the blocks, before the last '''print statement'''.
+
|Let us add ''' my $fname = within double quotes John semicolon''' outside the blocks, before the last '''print''' statement.
−
 
+
Save the changes.
−
Save the changes
+
  
 
|-
 
|-
Line 174: Line 178:
 
|-
 
|-
 
| 04:28
 
| 04:28
−
|Analyse the output that is displayed.
+
|Analyze the output that is displayed.
  
 
|-
 
|-
 
| 04:32
 
| 04:32
−
| Hope you are able to understand the scope of using''' my variable '''within a block and outside a block.
+
| Hope you are able to understand the scope of using 'my' variable within a block and outside a block.
  
 
|-
 
|-
 
| 04:41
 
| 04:41
−
| Next we will see about '''dynamically scoped variable''' in '''Perl'''.
+
| Next, we will see about '''dynamically scoped variable''' in '''Perl'''.
  
 
|-
 
|-
 
|04:47
 
|04:47
−
|'''Local keyword''' gives a temporary scope to a '''global variable'''.
+
|'''Local''' keyword gives a temporary scope to a '''global''' variable.
  
 
|-
 
|-
 
| 04:52
 
| 04:52
−
| The '''variable''' is visible to any '''function''' called from the original block.
+
| The variable is visible to any '''function''' called from the original block.
  
 
|-
 
|-
 
|04:58
 
|04:58
−
|You can declare a '''local variable '''as,
+
|You can declare a '''local''' variable as:
−
 
+
 
'''local $fValue = 100 semicolon'''
 
'''local $fValue = 100 semicolon'''
−
 
+
'''local $fname =  within double quotes "Rakesh" semicolon'''
−
'''local $fname”''' =  within double quotes '''Rakesh semicolon'''
+
  
 
|-
 
|-
 
|05:13
 
|05:13
−
|Let us understand this using a sample program.
+
|Let us understand this, using a sample program.
  
 
|-
 
|-
 
|05:17
 
|05:17
−
|Open the '''terminal''' and type '''gedit scope-local dot pl ampersand''' and press '''Enter'''.
+
|Open the '''terminal''' and type: '''gedit scope hyphen local dot pl ampersand''' and press '''Enter'''.
  
 
|-
 
|-
 
|05:27
 
|05:27
−
|This will open''' scope-local dot pl''' file in''' gedit'''.
+
|This will open''' scope hyphen local dot pl''' file, in''' gedit'''.
  
 
|-
 
|-
 
| 05:33
 
| 05:33
−
| Type the following code as displayed on the screen.
+
| Type the following code as displayed on the screen. Let me explain the code now.
−
 
+
−
Let me explain the code now.
+
  
 
|-
 
|-
 
|05:40
 
|05:40
−
|Here, in the first line we have declared a '''variable $fname '''and initialised it.
+
|Here, in the first line, we have declared a variable '''$fname '''and initialized it.
  
 
|-
 
|-
 
|05:47
 
|05:47
−
|Inside the '''function Welcome, '''we have declared a '''local variable '''by the same name,''' $fname.'''
+
|Inside the function '''Welcome()''', we have declared a '''local''' variable by the same name,''' $fname.'''
  
 
|-
 
|-
 
| 05:54
 
| 05:54
−
| Notice the '''local keyword''' before the '''variable '''name.
+
| Notice the '''local''' keyword before the variable name
  
 
|-
 
|-
 
| 05:59
 
| 05:59
−
| And we have assigned the value "'''Rakesh'''" to this '''variable.'''
+
| and we have assigned the value "Rakesh" to this variable.
  
 
|-
 
|-
 
| 06:03
 
| 06:03
−
| So, basically, inside function '''Welcome(), $fname''' is modified as a new temporary '''local variable.'''
+
| So, basically, inside function '''Welcome(), $fname''' is modified as a new temporary '''local''' variable.Then, the function '''Hello() '''is being '''call'''ed.
−
 
+
−
Then, the '''function Hello '''is being '''called'''.
+
  
 
|-
 
|-
 
|06:15
 
|06:15
−
|Here is the '''function definition '''of '''Hello.'''
+
|Here is the function definition of '''Hello()'''.
  
 
|-
 
|-
 
|06:18
 
|06:18
−
|At the end of the program, we are calling both the '''functions Welcome '''and '''Hello'''.
+
|At the end of the program, we are calling both the functions '''Welcome()''' and '''Hello()'''.
  
 
|-
 
|-
Line 258: Line 256:
 
|-
 
|-
 
|06:31
 
|06:31
−
|Switch back to the '''terminal''' and type, '''perl scope-local.pl''' and press '''Enter'''.
+
|Switch back to the '''terminal''' and type: '''perl scope hyphen local.pl''' and press '''Enter'''.
  
 
|-
 
|-
 
|06:41
 
|06:41
−
|The output is displayed as '''Hello, Rakesh !''' '''Hello, Welcome to Spoken tutorials!'''
+
|The output is displayed as:
 +
"Hello, Rakesh"!
 +
"Hello, Welcome to Spoken tutorials!"
  
 
|-
 
|-
Line 270: Line 270:
 
|-
 
|-
 
|06:51
 
|06:51
−
|When the function '''Welcome()''' is called, the '''function Hello()''' within it, accesses the '''local variable'''.
+
|When the function '''Welcome()''' is called, the function '''Hello()''' within it, accesses the '''local''' variable.
  
 
|-
 
|-
 
| 06:59
 
| 06:59
−
|Within '''Welcome(), $fname''' has the value "'''Rakesh'''".
+
|Within '''Welcome(), $fname''' has the value "Rakesh".
  
 
|-
 
|-
 
| 07:04
 
| 07:04
−
|After this, the '''function Hello() '''accesses the '''variable $fname '''once again'''.'''
+
|After this, the function '''Hello() '''accesses the variable '''$fname '''once again.
  
 
|-
 
|-
 
| 07:11
 
| 07:11
−
|But this time, it is the '''variable $fname '''which was initialized to''' "Welcome to spoken tutorials".'''
+
|But this time, it is the variable '''$fname '''which was initialized to "Welcome to spoken tutorials".
  
 
|-
 
|-
 
| 07:19
 
| 07:19
−
|It does not access the '''local variable $fname '''within the function '''Welcome().'''
+
|It does not access the local variable '''$fname '''within the function '''Welcome()'''.
  
 
|-
 
|-
 
| 07:25
 
| 07:25
−
|Which means that, the '''local variable '''restores the '''scope''', after leaving the block '''Welcome()'''.
+
|Which means that, the local variable restores the '''scope''', after leaving the block '''Welcome()'''.
 
|-
 
|-
 
| 07:32
 
| 07:32
−
| Next, we will see about '''global variables''' in '''Perl'''.
+
| Next, we will see about '''global''' variables in '''Perl'''.
  
 
|-
 
|-
Line 301: Line 301:
 
|-
 
|-
 
|07:43
 
|07:43
−
|'''Global variables '''are declared with''' our keyword'''.
+
|'''Global variables '''are declared with 'our' keyword.
  
 
|-
 
|-
 
| 07:47
 
| 07:47
−
|Here are some examples. '''our $fvalue = 100 semicolon </nowiki>''' '''our $fname ="Priya" semicolon'''
+
|Here are some examples.
 +
'''our $fvalue = 100 semicolon </nowiki>'''
 +
'''our $fname =within double quotes Priya semicolon'''
  
 
|-
 
|-
 
|08:01
 
|08:01
−
|Now let us look at a working example of '''global variables'''.
+
|Now, let us look at a working example of '''global''' variables.
  
 
|-
 
|-
 
|08:06
 
|08:06
−
|Switch back to the '''terminal '''and type '''gedit scope-our dot pl ampersand and '''press''' Enter'''
+
|Switch back to the '''terminal '''and type: '''gedit scope hyphen our dot pl ampersand''' and press''' Enter'''.
  
 
|-
 
|-
 
|08:16
 
|08:16
−
|This will open the file''' scope-our.pl''' in '''gedit'''.
+
|This will open the file''' scope hyphen our.pl''' in '''gedit'''.
  
 
|-
 
|-
Line 325: Line 327:
 
|-
 
|-
 
|08:27
 
|08:27
−
|I have declared '''package main '''and a '''global variable''' as''' our $i '''and I have initialised it to '''100;'''
+
|I have declared '''package main '''and a global variable as''' our $i '''and I have initialized it to '''100'''.
  
 
|-
 
|-
Line 333: Line 335:
 
|-
 
|-
 
| 08:40
 
| 08:40
−
|A '''package''' is a collection of code, which has its own '''namespace'''.
+
|A '''package''' is a collection of code which has its own '''namespace'''.
  
 
|-
 
|-
Line 345: Line 347:
 
|-
 
|-
 
|08:56
 
|08:56
−
|Within '''package First,''' the '''global variable "i"''' holds the value 10.
+
|Within '''package First,''' the global variable "i" holds the value 10.
  
 
|-
 
|-
 
|09:02
 
|09:02
−
|In '''package Second,''' the '''global variable "i" '''is assigned the value 20.
+
|In '''package Second,''' the global variable "i" is assigned the value 20.
  
 
|-
 
|-
 
|09:08
 
|09:08
−
|The main '''package '''uses both '''package First variable '''and the '''package Second variable'''.
+
|The '''main package '''uses both '''package First variable '''and the '''package Second variable'''.
  
 
|-
 
|-
 
| 09:15
 
| 09:15
−
|In my program, I have declared the same variable '''"i"''' in all the '''packages'''.
+
|In my program, I have declared the same variable "i" in all the '''packages'''.
  
 
|-
 
|-
 
| 09:21
 
| 09:21
−
|The '''package variable''' is referred by '''package name::variable name'''
+
|The '''package variable''' is referred by '''package name colon colon variable name'''.
  
 
|-
 
|-
 
| 09:29
 
| 09:29
−
|In our example it is''' $First::i, $Second::i'''
+
|In our example, it is''' $First colon colon i, $Second colon colon i'''.
  
 
|-
 
|-
 
| 09:39
 
| 09:39
−
|We have multiple '''packages '''within one file, and the '''global variable '''will be accessed by all the '''packages'''.
+
|We have multiple '''packages '''within one file and the global variable will be accessed by all the '''packages'''.
  
 
|-
 
|-
Line 377: Line 379:
 
|-
 
|-
 
|09:51
 
|09:51
−
|So, switch to '''terminal '''and type- '''perl scope-our dot pl''' and press '''Enter'''.
+
|So, switch to '''terminal '''and type: '''perl scope hyphen our dot pl''' and press '''Enter'''.
  
 
|-
 
|-
Line 389: Line 391:
 
|-
 
|-
 
|10:11
 
|10:11
−
|This brings us to the end of this tutorial. Let us summarise.
+
|This brings us to the end of this tutorial. Let us summarize.
  
 
|-
 
|-
 
| 10:16
 
| 10:16
 
|In this tutorial, we learnt:
 
|In this tutorial, we learnt:
−
 
+
scope of variables
−
* scope of variables
+
declaration of '''private variables'''
−
* declaration of '''private variables'''
+
'''dynamically scoped variables''' and
−
* '''dynamically scoped variables''' and
+
'''global variables''' with examples.<br/>  
−
* '''global variables''' with examples.<br/>  
+
  
 
|-
 
|-
 
| 10:29
 
| 10:29
−
|It is preferred to use''' my''' than''' local''' as the compilation is faster.
+
|It is preferred to use 'my' than '''local''', as the compilation is faster.
  
 
|-
 
|-
Line 414: Line 415:
 
|-
 
|-
 
| 10:42
 
| 10:42
−
| Declare a package as '''FirstModule'''
+
| Declare a '''package''' as '''FirstModule'''.
  
 
|-
 
|-
 
| 10:46
 
| 10:46
−
| Declare a variable '''$age''' as '''our''' and assign the value '''42'''
+
| Declare a variable '''$age''' as '''our''' and assign the value '''42'''.
  
 
|-
 
|-
 
| 10:52
 
| 10:52
−
|Declare another package as '''SecondModule'''
+
|Declare another package as '''SecondModule'''.
  
 
|-
 
|-
 
| 10:56
 
| 10:56
−
|Declare a variable '''$ageword''' as '''our''' and assign the value within double quotes '''"Forty-Two"'''
+
|Declare a variable '''$ageword''' as '''our''' and assign the value within double quotes "Forty-Two".
  
 
|-
 
|-
 
| 11:05
 
| 11:05
−
| Declare a subroutine''' First()'''
+
| Declare a subroutine''' First()'''.
  
 
|-
 
|-
Line 438: Line 439:
 
|-
 
|-
 
| 11:16
 
| 11:16
−
|''local''' '''$age = 52''' semicolon
+
|'''local''' '''$age = 52''' semicolon
  
 
|-
 
|-
 
| 11:20
 
| 11:20
−
|'''my''' '''$ageword''' = within double quotes '''Fifty-two;'''
+
|'''my''' '''$ageword''' = within double quotes '''Fifty-two semicolon '''
  
 
|-
 
|-
 
| 11:27
 
| 11:27
−
|Call another subroutine as '''Result()'''
+
|Call another subroutine as '''Result()'''.
  
 
|-
 
|-
Line 454: Line 455:
 
|-
 
|-
 
| 11:37
 
| 11:37
−
|End the subroutine
+
|End the subroutine.
  
 
|-
 
|-
 
| 11:39
 
| 11:39
−
| Declare the subroutine '''Result()'''
+
| Declare the subroutine '''Result()'''.
  
 
|-
 
|-
 
| 11:42
 
| 11:42
−
| Again print the values of '''$age''' and '''$ageword'''
+
| Again print the values of '''$age''' and '''$ageword'''.
  
 
|-
 
|-
 
| 11:47
 
| 11:47
−
| End the subroutine
+
| End the subroutine.
  
 
|-
 
|-
 
| 11:49
 
| 11:49
−
| Call the function '''First()'''
+
| Call the function '''First()'''.
  
 
|-
 
|-
Line 478: Line 479:
 
|-
 
|-
 
|11:57
 
|11:57
−
|The video at the following link summarises the Spoken Tutorial project.
+
|The video at the following link summarizes the '''Spoken Tutorial''' project.
−
 
+
 
Please download and watch it.
 
Please download and watch it.
  
 
|-
 
|-
 
|12:05
 
|12:05
−
|The Spoken Tutorial Project Team conducts workshops and gives certificates for those who pass an online test.
+
|The '''Spoken Tutorial''' project team conducts workshops and gives certificates for those who pass an online test.
−
 
+
 
For more details, please write to us.
 
For more details, please write to us.
  
Line 495: Line 494:
 
|-
 
|-
 
|12:31
 
|12:31
−
|This is Nirmala Venkat from IIT Bombay, signing off. Thanks for watching.
+
|This is Nirmala Venkat from '''IIT Bombay''', signing off. Thanks for watching.
  
 
|}
 
|}

Latest revision as of 18:12, 20 February 2017

Time
Narration
00:01 Welcome to the Spoken Tutorial on Access Modifiers in PERL.
00:07 In this tutorial, we will learn about:

Scope of variables Private variables Dynamically scoped variables Global variables

00:19 For this tutorial, I am using:

Ubuntu Linux 12.04 operating system Perl 5.14.2 and the gedit Text Editor.

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 Analyze 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 initialized 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 initialized 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 summarize.
10:16 In this tutorial, we learnt:

scope of variables declaration of private variables dynamically scoped variables and global variables with examples.

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 summarizes 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.

Contributors and Content Editors

PoojaMoolya, Sandhya.np14

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