Difference between revisions of "PERL/C2/Blocks-in-Perl/English-timed"

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| 00:01
 
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|Welcome to the spoken tutorial on ''' BLOCKS''' in Perl.  
+
|Welcome to the spoken tutorial on ''' Blocks in Perl'''.  
  
 
|-
 
|-
 
| 00:06
 
| 00:06
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| In this tutorial, we will learn about the various ''' BLOCKS''' available in '''Perl'''
+
| In this tutorial, we will learn about the various ''' blocks''' available in '''Perl'''
  
 
|-
 
|-
 
|00:13
 
|00:13
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|I am using ''' Ubuntu Linux 12.04''' operating system and ''' Perl 5.14.2'''
+
|I am using ''' Ubuntu Linux 12.04''' operating system and ''' Perl 5.14.2'''.
 
   
 
   
 
|-
 
|-
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|-
 
|-
 
|00:31
 
|00:31
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|As a pre-requisite, you should have basic knowledge of '''Variables, Comments''' in ''' Perl '''  
+
|As a pre-requisite, you should have basic knowledge of '''variables, comments''' in ''' Perl.'''  
  
 
|-
 
|-
 
| 00:38
 
| 00:38
−
| Knowledge of ''' Data structures''' in '''PERL''' will be an added advantage.  
+
| Knowledge of '''data structures''' in '''PERL''' will be an added advantage.  
  
 
|-
 
|-
 
| 00:44
 
| 00:44
−
|Please go through the relevant spoken tutorials on the ''' spoken tutorial ''' website.  
+
|Please go through the relevant spoken tutorials on the '''Spoken Tutorial''' website.  
  
 
|-
 
|-
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|-
 
|-
 
| 01:01
 
| 01:01
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| '''BEGIN'''  
+
|* '''BEGIN'''  
 
   
 
   
 
|-
 
|-
 
|01:02
 
|01:02
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|'''END'''  
+
|*'''END'''  
 
   
 
   
 
|-
 
|-
 
|01:03
 
|01:03
−
|''' UNITCHECK'''
+
|*''' UNITCHECK'''
  
 
|-
 
|-
 
| 01:04
 
| 01:04
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| ''' CHECK. '''
+
|* ''' CHECK. '''
  
 
|-
 
|-
 
|01:05
 
|01:05
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|''' INIT '''
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|*''' INIT '''.
  
 
|-
 
|-
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|-
 
|-
 
|01:10
 
|01:10
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|''' BEGIN''' block get executed at the time of compilation.  
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|''' BEGIN''' block gets executed at the time of compilation.  
  
 
|-
 
|-
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|-
 
|-
 
| 01:31
 
| 01:31
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|That is in the ''' First define First execute ''' pattern  
+
|That is, in the 'First define First execute' pattern.
  
 
|-
 
|-
 
|01:35
 
|01:35
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|The syntax for ''' BEGIN block''' is as follows  
+
|The syntax for ''' BEGIN''' block is as follows:
 
   
 
   
 
|-
 
|-
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|-
 
|-
 
|01:51
 
|01:51
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| Press '''Enter '''
+
| Press '''Enter '''.
  
 
|-
 
|-
 
|01:52
 
|01:52
−
|Close curly bracket  
+
|Close curly bracket.
 
   
 
   
 
|-
 
|-
 
|01:55
 
|01:55
−
|Now, let us look at an example of '''BEGIN''' blocks.  
+
|Now, let us look at an example of '''BEGIN''' block.  
 
   
 
   
 
|-
 
|-
 
|01:59
 
|01:59
−
|Open the Terminal and type  
+
|Open the Terminal and type:
  
 
|-
 
|-
 
|02:02
 
|02:02
−
| ''' gedit beginBlock dot pl ''' space '''ampersand'''
+
| '''gedit beginBlock dot pl ''' space '''ampersand'''
  
 
|-
 
|-
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|-
 
|-
 
|02:24
 
|02:24
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|Here, we have printed some text before and after ''' BEGIN''' blocks.  
+
|Here, we have printed some text before and after '''BEGIN''' blocks.  
 
   
 
   
 
|-
 
|-
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|-
 
|-
 
| 02:42
 
| 02:42
−
|Putting a semicolon, will result in a syntax error, on execution of the program.  
+
|Putting a semicolon will result in a syntax error on execution of the program.  
 
   
 
   
 
|-
 
|-
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|-
 
|-
 
| 02:53
 
| 02:53
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| Then switch to  terminal and execute the script by typing,
+
| Then switch to  terminal and execute the script by typing:
 
   
 
   
 
|-
 
|-
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|-
 
|-
 
|  03:09
 
|  03:09
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| Notice that The line written inside the first '''BEGIN''' block gets printed first and  
+
| Notice that the line written inside the first '''BEGIN''' block gets printed first and  
 
   
 
   
 
|-
 
|-
 
|03:16
 
|03:16
−
| The first '''print statement''' in the script actually gets printed after the '''BEGIN block statements. '''
+
| the first '''print statement''' in the script actually gets printed after the '''BEGIN''' block statements.
 
    
 
    
 
|-
 
|-
 
|  03:25
 
|  03:25
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| '''BEGIN blocks''' gets executed in the order of their declaration.  
+
| '''BEGIN''' blocks get executed in the order of their declaration.  
  
 
|-
 
|-
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|-
 
|-
 
| 03:46
 
| 03:46
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| '''BEGIN blocks'''  always get executed in the '''First In First Out''' manner.  
+
| '''BEGIN''' blocks always get executed in the 'First In First Out' manner.  
  
 
|-
 
|-
 
|03:52
 
|03:52
−
|So one of the use of this '''block''' is to include files inside a Perl script, before actual execution starts.  
+
|So, one of the use of this '''block''' is to include files inside a Perl script, before actual execution starts.  
  
 
|-
 
|-
 
|04:01
 
|04:01
−
|Now, let us understand the '''END block '''
+
|Now, let us understand the '''END''' block.
 
   
 
   
 
|-
 
|-
 
|04:04
 
|04:04
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|''' END block''' get executed at the end of PERL program  
+
|'''END''' block gets executed at the end of PERL program.
  
 
|-
 
|-
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|-
 
|04:17
 
|04:17
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|We can have several ''' END blocks'''  inside a '''Perl script.'''  
+
|We can have several ''' END''' blocks inside a '''Perl script.'''  
  
 
|-
 
|-
 
|04:21
 
|04:21
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|These blocks will get executed in reverse order of declaration  
+
|These blocks will get executed in reverse order of declaration.
 
   
 
   
 
|-
 
|-
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|-
 
|-
 
|04:30
 
|04:30
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|The syntax for ''' END block''' is as follows  
+
|The syntax for ''' END''' block is as follows:
  
 
|-
 
|-
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|-
 
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|04:39
 
|04:39
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|Press ''' Enter'''  
+
|Press ''' Enter'''.
  
 
|-
 
|-
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|-
 
|-
 
|04:45
 
|04:45
−
|Press ''' Enter'''
+
|Press ''' Enter'''.
  
 
|-
 
|-
 
|04:46
 
|04:46
−
|Close curly bracket  
+
|Close curly bracket.
  
 
|-
 
|-
 
|04:49
 
|04:49
−
|Now let us look at an example of END blocks.  
+
|Now, let us look at an example of END blocks.  
 
   
 
   
 
|-
 
|-
 
|04:53
 
|04:53
−
|Open the Terminal and type  
+
|Open the Terminal and type:
  
 
|-
 
|-
 
|  04:56
 
|  04:56
−
|''' gedit endBlock dot pl space ampersand'''
+
|'''gedit endBlock dot pl''' space ampersand
  
 
|-
 
|-
 
|  05:00
 
|  05:00
−
|and press '''Enter'''
+
|and press '''Enter'''.
  
 
|-
 
|-
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|-
 
|-
 
|07:50
 
|07:50
−
|Press '''Enter'''
+
|Press '''Enter'''.
  
 
|-
 
|-
 
|07:52
 
|07:52
−
|Close curly bracket  
+
|Close curly bracket.
  
 
|-
 
|-
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|-
 
|-
 
|08:07
 
|08:07
−
|Press '''Enter '''
+
|Press '''Enter '''.
  
 
|-
 
|-
 
|08:08
 
|08:08
−
|Close curly bracket  
+
|Close curly bracket.
  
 
|-
 
|-
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|-
 
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|08:21
 
|08:21
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|Piece of code to be initialised
+
|Piece of code to be initialized
  
 
|-
 
|-
 
|08:24
 
|08:24
−
|Press '''Enter '''
+
|Press '''Enter '''.
  
 
|-
 
|-
 
|08:26
 
|08:26
−
|Close curly bracket  
+
|Close curly bracket.
  
 
|-
 
|-
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|-
 
|-
 
|08:37
 
|08:37
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|In this tutorial, we have learnt -
+
|In this tutorial, we have learnt: 
  
 
|-
 
|-
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|08:48
 
|08:48
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|using sample programs  
+
|using sample programs.
  
 
|-
 
|-
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|-
 
|-
 
|09:02
 
|09:02
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|Watch the video available at the following link
+
|Watch the video available at the following link.
 
    
 
    
 
|-
 
|-
 
|09:06
 
|09:06
−
|It summaries the Spoken Tutorial project
+
|It summarizes the Spoken Tutorial project.
 
   
 
   
 
|-
 
|-
 
|09:09
 
|09:09
−
|If you do not have good bandwidth, you can download and watch it
+
|If you do not have good bandwidth, you can download and watch it.
 
   
 
   
 
|-
 
|-
 
| 09:14
 
| 09:14
−
|  The Spoken Tutorial Project Team  Conducts workshops using spoken tutorials
+
|  The Spoken Tutorial project team: Conducts workshops using spoken tutorials.
 
    
 
    
 
|-
 
|-
 
|09:20
 
|09:20
−
|Gives certificates to those who pass an online test
+
|Gives certificates to those who pass an online test.
 
   
 
   
 
|-
 
|-
 
|09:24
 
|09:24
−
|For more details, please write to contact at spoken hyphen tutorial dot org
+
|For more details, please write to contact at: spoken hyphen tutorial dot org.
 
   
 
   
 
|-
 
|-
 
| 09:32
 
| 09:32
−
|  Spoken Tutorial Project is a part of the Talk to a Teacher project
+
|  "Spoken Tutorial" project is a part of the "Talk to a Teacher" project.
 
   
 
   
 
|-
 
|-
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|-
 
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|09:45
 
|09:45
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|More information on this Mission is available at spoken hyphen tutorial dot org slash NMEICT hyphen Intro
+
|More information on this mission is available at: spoken hyphen tutorial dot org slash NMEICT hyphen Intro.
 
   
 
   
 
|-
 
|-
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|10:00
 
|10:00
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|This is Amol signing off.
+
|This is Amol, signing off.
 
    
 
    
 
|-
 
|-

Revision as of 23:30, 13 May 2015

Time Narration
00:01 Welcome to the spoken tutorial on Blocks in Perl.
00:06 In this tutorial, we will learn about the various blocks available in Perl
00:13 I am using Ubuntu Linux 12.04 operating system and Perl 5.14.2.
00:21 I will also be using the gedit Text Editor.
00:26 You can use any text editor of your choice.
00:31 As a pre-requisite, you should have basic knowledge of variables, comments in Perl.
00:38 Knowledge of data structures in PERL will be an added advantage.
00:44 Please go through the relevant spoken tutorials on the Spoken Tutorial website.
00:50 Perl provides 5 special blocks.
00:53 These blocks get executed at various stages of a Perl program.
00:59 These blocks are:
01:01 * BEGIN
01:02 *END
01:03 * UNITCHECK
01:04 * CHECK.
01:05 * INIT .
01:06 Let us start with understanding the BEGIN block.
01:10 BEGIN block gets executed at the time of compilation.
01:15 So, any code written inside this block gets executed first during compilation.
01:22 We can have several BEGIN blocks inside a Perl script.
01:26 These blocks will get executed in the order of declaration.
01:31 That is, in the 'First define First execute' pattern.
01:35 The syntax for BEGIN block is as follows:
01:40 BEGIN in capital letters space open curly bracket
01:45 Press Enter.
01:47 Piece of code to be executed at the time of compilation
01:51 Press Enter .
01:52 Close curly bracket.
01:55 Now, let us look at an example of BEGIN block.
01:59 Open the Terminal and type:
02:02 gedit beginBlock dot pl space ampersand
02:08 and press Enter.
02:10 This will open the beginBlock dot pl file in gedit.
02:15 Type the following piece of code as displayed on the screen.
02:20 Let us look at what I have written inside the script.
02:24 Here, we have printed some text before and after BEGIN blocks.
02:31 Similarly, I have written one print statement in each BEGIN block.
02:37 Please note, I have not given the semicolon after the BEGIN blocks.
02:42 Putting a semicolon will result in a syntax error on execution of the program.
02:49 Now, press Ctrl+s to save the file.
02:53 Then switch to terminal and execute the script by typing:
02:58 perl beginBlock dot pl
03:01 and press Enter.
03:04 You will get the output as displayed on the terminal.
03:09 Notice that the line written inside the first BEGIN block gets printed first and
03:16 the first print statement in the script actually gets printed after the BEGIN block statements.
03:25 BEGIN blocks get executed in the order of their declaration.
03:31 From this example, it is evident that:
03:34 The code written inside the BEGIN blocks gets executed first.
03:40 This is irrespective of the location of the BEGIN block inside PERL script.
03:46 BEGIN blocks always get executed in the 'First In First Out' manner.
03:52 So, one of the use of this block is to include files inside a Perl script, before actual execution starts.
04:01 Now, let us understand the END block.
04:04 END block gets executed at the end of PERL program.
04:09 Code written inside this block gets executed after PERL has finished executing the program.
04:17 We can have several END blocks inside a Perl script.
04:21 These blocks will get executed in reverse order of declaration.
04:26 That is, in Last define First execute pattern.
04:30 The syntax for END block is as follows:
04:35 END in capital letters open curly bracket
04:39 Press Enter.
04:40 Piece of code to be executed at the end of the PERL script
04:45 Press Enter.
04:46 Close curly bracket.
04:49 Now, let us look at an example of END blocks.
04:53 Open the Terminal and type:
04:56 gedit endBlock dot pl space ampersand
05:00 and press Enter.
05:03 This will open the endBlock dot pl file in gedit.
05:08 Type the following piece of code as displayed on the screen.
05:13 Let us look at what I have written inside this script.
05:17 Here we have printed some text before and after END blocks.
05:23 Similarly, we have written one print statement in each END block.
05:29 Please note, I have not given the semicolon after the END block.
05:34 If we give the semicolon, there will be a syntax error on compilation.
05:41 Now, press Ctrl+s to save the file.
05:45 Then switch to terminal and execute the script by typing,
05:50 perl endBlock dot pl
05:53 and press Enter.
05:55 You will get the output as displayed on the terminal.
06:00 Notice that : The line written inside the END block is printed last.
06:06 The last print statement in the script actually gets printed before the END block statements and
06:13 END blocks gets executed in the reverse order of their declaration.
06:20 From the example, it is evident that
06:23 The code written inside the END blocks get executed at the end.
06:29 This is irrespective of the location of the END block inside the PERL script and
06:36 END blocks gets executed in the Last In First Out manner.
06:41 So, one use of END block is to destroy objects created in the program, before exiting.
06:49 Similarly, PERL has UNITCHECK, CHECK and INIT blocks.
06:55 These blocks are used rarely by developers and are a bit difficult to understand.
07:02 So, I will be just briefing you about these blocks.
07:06 UNITCHECK, CHECK and INIT blocks are useful-
07:10 to catch the transition between compilation and execution phase of the main program and
07:18 to perform some checks or initialisation, after compilation and before execution
07:24 UNITCHECK and CHECK blocks runs in Last in First out manner
07:31 whereas INIT block runs in First In First Out manner.
07:37 The syntax for UNITCHECK block is as follows
07:41 UNITCHECK in capital letters space open curly bracket
07:46 Press Enter
07:48 Piece of code to be executed
07:50 Press Enter.
07:52 Close curly bracket.
07:54 The syntax for CHECK block is as follows
07:58 CHECK in capital letters space open curly bracket
08:03 Press Enter
08:04 Piece of code to be executed
08:07 Press Enter .
08:08 Close curly bracket.
08:11 The syntax for INIT block is as follows
08:15 INIT in capital letters space open curly bracket
08:20 Press Enter
08:21 Piece of code to be initialized
08:24 Press Enter .
08:26 Close curly bracket.
08:28 For better understanding, I recommend that you experiment with these blocks in your Perl scripts.
08:36 Let us summarize.
08:37 In this tutorial, we have learnt:
08:40 BEGIN and END blocks in detail and
08:44 Introduction to UNITCHECK, CHECK and INIT blocks
08:48 using sample programs.
08:52 Here is assignment for you -
08:54 Type the below code inside a PERL script;
08:58 Execute the script and observe the output.
09:02 Watch the video available at the following link.
09:06 It summarizes the Spoken Tutorial project.
09:09 If you do not have good bandwidth, you can download and watch it.
09:14 The Spoken Tutorial project team: Conducts workshops using spoken tutorials.
09:20 Gives certificates to those who pass an online test.
09:24 For more details, please write to contact at: spoken hyphen tutorial dot org.
09:32 "Spoken Tutorial" project is a part of the "Talk to a Teacher" project.
09:37 It is supported by the National Mission on Education through ICT, MHRD, Government of India.
09:45 More information on this mission is available at: spoken hyphen tutorial dot org slash NMEICT hyphen Intro.
09:57 Hope you enjoyed this Perl tutorial.
10:00 This is Amol, signing off.
10:02 Thanks for joining.

Contributors and Content Editors

Gaurav, PoojaMoolya, Sandhya.np14

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