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

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| In this tutorial, we will learn about the various ''' blocks''' available in '''Perl'''
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| In this tutorial, we will learn about the various ''' blocks''' available in '''Perl'''.
  
 
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|*'''END'''  
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|* '''END'''  
 
   
 
   
 
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|Piece of code to be executed at the time of compilation  
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|Piece of code to be executed at the time of compilation,
 
    
 
    
 
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|-
 
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|01:51
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| Press '''Enter '''.
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| press '''Enter '''.
  
 
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| Similarly, I have written one ''' print statement''' in each '''BEGIN''' block.  
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| Similarly, I have written one ''' print''' statement in each '''BEGIN''' block.  
  
 
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|Now, press ''' Ctrl+s''' to save the file.  
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|Now, press ''' Ctrl+s''' to '''save''' the file.  
 
   
 
   
 
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| the first '''print statement''' in the script actually gets printed after the '''BEGIN''' block statements.  
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| the first '''print''' statement in the script actually gets printed after the '''BEGIN''' block statements.  
 
    
 
    
 
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| This is irrespective of the location of the ''' BEGIN''' block inside ''' PERL''' script.  
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| This is irrespective of the location of the ''' BEGIN''' block inside PERL  script.  
  
 
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|-
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|The syntax for ''' END''' block is as follows:  
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|The syntax for '''END''' block is as follows:  
  
 
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|-
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|-
 
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|04:39
 
|04:39
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|Press ''' Enter'''.  
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|press ''' Enter'''.  
  
 
|-
 
|-
 
|04:40
 
|04:40
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|Piece of code to be executed at the end of the ''' PERL ''' script  
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|Piece of code to be executed at the end of the ''' PERL ''' script,
 
   
 
   
 
|-
 
|-
 
|04:45
 
|04:45
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|Press ''' Enter'''.
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|press ''' Enter'''.
  
 
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|  05:23
 
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|Similarly, we have written one print statement in each ''' END''' block.  
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|Similarly, we have written one '''print''' statement in each ''' END''' block.  
  
 
|-
 
|-
 
|  05:29
 
|  05:29
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| Please note, I have not given the ''' semicolon''' after the '''END''' block.  
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| Please note, I have not given the semicolon after the '''END''' block.  
  
 
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|  05:41
 
|  05:41
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| Now, press ''' Ctrl+s''' to save the file.  
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| Now, press ''' Ctrl+s''' to '''save''' the file.  
 
   
 
   
 
|-
 
|-
 
|  05:45
 
|  05:45
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| Then switch to terminal and execute the script by typing,
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| Then switch to terminal and execute the script by typing:
  
 
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|and '''press Enter.'''
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|and press '''Enter.'''
  
 
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| The last ''' print statement''' in the script actually gets printed before the '''END block statements and  
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| The last '''print''' statement in the script actually gets printed before the '''END''' block statements and  
  
 
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| 06:13
 
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| ''' END''' blocks gets executed in the reverse order of their declaration.  
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| '''END''' blocks get executed in the reverse order of their declaration.  
  
 
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|The code written inside the ''' END''' blocks get executed at the end.  
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|the code written inside the '''END''' blocks get executed at the end.  
 
   
 
   
 
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|06:29
 
|06:29
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| This is irrespective of the location of the ''' END''' block inside the '''PERL''' script and  
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| This is irrespective of the location of the '''END''' block inside the PERL script and  
 
   
 
   
 
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|06:36
 
|06:36
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|'''END''' blocks gets executed in the ''' Last In First Out''' manner.  
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|'''END''' blocks get executed in the '''Last In First Out''' manner.  
  
 
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|06:41
 
|06:41
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|So, one use of '''END''' block is to destroy objects created in the program, before exiting.  
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|So, one use of '''END''' block is to destroy objects created in the program before exiting.  
 
 
 
 
 
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| Similarly, ''' PERL''' has ''' UNITCHECK, CHECK''' and ''' INIT''' blocks.  
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| Similarly, PERL has '''UNITCHECK, CHECK''' and '''INIT''' blocks.  
  
 
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|''' UNITCHECK, CHECK''' and '''INIT''' blocks are useful-
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|''' UNITCHECK, CHECK''' and '''INIT''' blocks are useful:
 
   
 
   
 
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|to perform some checks or initialisation, after compilation and before execution  
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|to perform some checks or initialization, after compilation and before execution.
  
 
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|''' UNITCHECK''' and '''CHECK''' blocks runs in '''Last in First out''' manner   
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|''' UNITCHECK''' and '''CHECK''' blocks run in '''Last in First out''' manner   
  
 
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|whereas '''INIT''' block runs in '''First In First Out''' manner.  
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|whereas '''INIT''' block runs in '''First In First Out''' manner.  
  
 
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|The syntax for '''UNITCHECK''' block is as follows  
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|The syntax for '''UNITCHECK''' block is as follows:
  
 
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|Press '''Enter'''  
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|press '''Enter'''.
  
 
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|07:48
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|Piece of code to be executed  
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|Piece of code to be executed,
  
 
|-
 
|-
 
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|07:50
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|Press '''Enter'''.
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|press '''Enter'''.
  
 
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|The syntax for '''CHECK''' block is as follows
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|The syntax for '''CHECK''' block is as follows:
  
 
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|Press '''Enter'''  
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|press '''Enter'''.
  
 
|-
 
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|08:04
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|Piece of code to be executed  
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|Piece of code to be executed,
  
 
|-
 
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|08:07
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|Press '''Enter '''.
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|press '''Enter'''.
  
 
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|The syntax for '''INIT''' block is as follows  
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|The syntax for '''INIT''' block is as follows:
  
 
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|''' INIT''' in capital letters space open curly bracket  
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|'''INIT''' in capital letters space open curly bracket  
  
 
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|08:20
 
|08:20
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|Press '''Enter '''
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|press '''Enter'''.
  
 
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|08:21
 
|08:21
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|Piece of code to be initialized  
+
|Piece of code to be initialized,
  
 
|-
 
|-
 
|08:24
 
|08:24
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|Press '''Enter '''.
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|press '''Enter '''.
  
 
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|08:40
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|''' BEGIN''' and '''END''' blocks in detail and  
+
|'''BEGIN''' and '''END''' blocks in detail and  
  
 
|-
 
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|08:44
 
|08:44
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|Introduction to ''' UNITCHECK, CHECK''' and '''INIT ''' blocks  
+
|introduction to '''UNITCHECK, CHECK''' and '''INIT''' blocks  
  
 
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|Here is assignment for you -
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|Here is an assignment for you: 
  
 
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|Execute the script and observe the output.  
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|execute the script and observe the output.  
  
 
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| 09:57
 
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|  Hope you enjoyed this Perl tutorial.  
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|  Hope you enjoyed this '''Perl''' tutorial.  
 
   
 
   
 
|-
 
|-

Revision as of 10:55, 14 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 get 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 get 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 initialization, after compilation and before execution.
07:24 UNITCHECK and CHECK blocks run 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 an 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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