PoojaMoolya at 07:32, 17 June 2014

2014-06-17T07:32:03Z

AmolBrahmankar: Created page with ''''Title Of Script: '''BLOCKS in PERL '''Author:''' Amol Brahmankar '''Keywords:''' BLOCKS in perl video tutorial. {| style="border-spacing:0;" | style="border-top:0.0007in …'

2014-04-10T06:07:59Z

Created page with ''''Title Of Script: '''BLOCKS in PERL '''Author:''' Amol Brahmankar '''Keywords:''' BLOCKS in perl video tutorial. {| style="border-spacing:0;" | style="border-top:0.0007in …'

New page

'''Title Of Script: '''BLOCKS in PERL

'''Author:''' Amol Brahmankar

'''Keywords:''' BLOCKS in perl video tutorial.

{| style="border-spacing:0;"
| style="border-top:0.0007in solid #000000;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| <center>'''Visual Clue'''</center>
| style="border:0.0007in solid #000000;padding:0.0382in;"| <center>'''Narration'''</center>

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| Slide
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| Welcome to the spoken tutorial on BLOCKS in '''Perl'''

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| Slide: Learning Objectives
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| In this tutorial, we will learn about the various '''BLOCKS '''available in '''Perl'''

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| Slide: System Requirements
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| I am using '''Ubuntu Linux 12.04''' operating system and '''Perl 5.14.2'''

I will also be using the '''gedit '''Text Editor.

You can use any text editor of your choice.

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| Slide: Prerequisites
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| As a pre-requisite,

you should have basic knowledge of '''Variables, Comments '''in''' Perl'''

Knowledge of''' data structures in PERL '''will be an added advantage'''.'''

Please go through the relevant spoken tutorials on the '''spoken tutorial '''website.

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| Slide
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| Perl provides 5 special '''blocks'''.

These '''blocks '''get executed at various stages of a '''Perl '''program.

These blocks are:

# BEGIN
# END
# UNITCHECK
# CHECK
# INIT

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"|
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| Let us start with understanding the '''BEGIN''' block

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| Slide
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| * '''BEGIN''' block get executed at the time of compilation.
* So, any code written inside this block gets executed first during compilation.
* We can have several '''BEGIN''' blocks inside a '''Perl '''script.
* These blocks will get executed in the order of declaration.
* That is in the '''First define First execute '''pattern

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| Slide

'''BEGIN {'''

'''<nowiki># Piece of code to be executed at the time of compilation</nowiki>'''

'''}'''
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| The syntax for '''BEGIN''' block''' '''is as follows

'''BEGIN''' in capital letters space open curly bracket

'''Press Enter'''

Piece of code to be executed at the time of compilation

'''Press Enter'''

Close curly bracket

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"|
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| Now let us look at an example of '''BEGIN '''blocks.

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| Switch to the Terminal and type

'''gedit beginBlock.pl '''and press '''Enter'''.
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| Open the '''Terminal''' and type

'''gedit beginBlock dot pl space ampersand'''

and press''' Enter'''

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| Gedit

'''<nowiki>#!/usr/bin/perl </nowiki>'''

'''print "First Line in PERL script\n"; '''

'''BEGIN { '''

'''print "Inside First BEGIN block\n"; '''

'''} '''

'''BEGIN { '''

'''print "Inside Second BEGIN block\n"; '''

'''} '''

'''BEGIN { '''

'''print "Inside Third BEGIN block\n"; '''

'''} '''

'''print "Last line in PERL script\n";'''

| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| This will open the '''beginBlock dot pl''' file in '''gedit'''.

Type the following piece of code as displayed on the screen.

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| '''Gedit'''
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| Let us look at what I have written inside the script.

* Here we have printed some text before and after the '''BEGIN''' blocks. 

* Similarly, I have written one '''print statement''' in each '''BEGIN''' block. 

* Please note, I have '''not''' given the '''semicolon''' after the '''BEGIN''' blocks. 

* Putting a semicolon, will result in a '''syntax error''' on execution of the program.

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| Press '''Ctrl S'''
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| Now, press '''ctrl+s''' to '''save''' the file.

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| Switch to terminal

'''perl beginBlock.pl'''

| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| Then switch to the '''terminal '''and execute the script by typing,

'''perl beginBlock dot pl'''

and press''' Enter.'''

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| Highlight the output on the terminal

Inside First BEGIN block

Inside Second BEGIN block

Inside Third BEGIN block

First Line in PERL script

Last line in PERL script
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| You will get the output as displayed on the '''terminal'''

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| Terminal
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| '''Notice that;'''

* The line written inside the first '''BEGIN''' '''block '''gets''' '''printed first and
* The first '''print statement''' in the script actually gets printed after the '''BEGIN block statements.'''
* '''BEGIN blocks''' gets executed in the order of their declaration.

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| Slide
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| From this example, it is evident that:

* The code written inside the '''BEGIN''' blocks get executed '''first'''.
* This is irrespective of the location of the '''BEGIN''' block inside '''PERL''' script.
* '''BEGIN blocks''' always get executed in the '''First In First Out''' manner

So one of the use of this '''block''' is to include files inside a '''Perl '''script, before actual execution starts.

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"|
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| Now, let us understand the '''END''' block

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| Slide
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| * '''END''' block get executed at the end of the '''PERL''' program
* Code written inside this '''block''' gets executed after '''PERL''' has finished executing the program
* We can have several '''END''' blocks inside a '''Perl''' script.
* These '''blocks''' will get executed in reverse order of definition.
* That is in '''Last define First execute''' pattern.

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| Slide

'''END {'''

'''<nowiki># Piece of code to be executed at the end of the PERL script</nowiki>'''

'''}'''
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| The syntax for '''END''' block''' '''is as follows

'''END''' in capital letters space open curly bracket

'''Press Enter'''

Piece of code to be executed at the end of the PERL script

'''Press Enter'''

Close curly bracket

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"|
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| Now let us look at an example of '''END '''blocks.

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| Switch to the Terminal and type

'''gedit endBlock.pl '''and press '''Enter'''.
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| Open the '''Terminal''' and type

'''gedit endBlock dot pl space ampersand'''

and press''' Enter'''

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| Gedit

'''<nowiki>#!/usr/bin/perl </nowiki>'''

'''print "First Line in PERL script\n"; '''

'''END { '''

'''print "Inside First END block\n"; '''

'''} '''

'''END { '''

'''print "Inside Second END block\n"; '''

'''} '''

'''END { '''

'''print "Inside Third END block\n"; '''

'''} '''

'''print "Last line in PERL script\n";'''

| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| This will open the '''endBlock dot pl''' file in '''gedit'''.

Type the following piece of code as displayed on the screen.

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| Gedit
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| Let us look at what I have written inside this script.

* Here we have printed some text before and after the '''END''' blocks. 

* Similarly, we have written one print statement in each '''END''' block. 

* Please note, I have not given the semicolon after the '''END''' block. 

* If we give the semicolon, there will be a syntax error on compilation.

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| Press '''Ctrl S'''
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| Now, press '''ctrl+s''' to '''save''' the file.

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| Switch to terminal

'''perl endBlock.pl'''

| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| Then switch to the '''terminal '''and execute the script by typing,

'''perl endBlock dot pl'''

and press''' Enter.'''

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| Highlight the output on the terminal

First Line in PERL script

Last line in PERL script

Inside Third END block

Inside Second END block

Inside First END block
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| You will get the output as displayed on the terminal

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| Terminal
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| Notice that;

* The line written inside the '''END''' block is printed last.
* The last '''print statement '''in the script actually gets printed before the '''END''' block statements and
* '''END blocks''' gets executed in the reverse order of their declaration

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| Slide
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| From the example, it is evident that;

* The code written inside the '''END''' blocks get executed at the end
* This is irrespective of the location of the '''END''' block inside the '''PERL '''script and
* '''END blocks''' gets executed in the '''Last In First Out '''manner

So, one use of''' END block''' is to destroy objects created in the program, before exiting.

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| Slide
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| Similarly '''PERL''' has '''UNITCHECK, CHECK''' and '''INIT''' blocks.

These blocks are used rarely by developers and are a bit difficult to understand.

So, I will be just brief you about these blocks.

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| Slide
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| '''UNITCHECK, CHECK '''and '''INIT''' blocks are useful;

* to catch the '''transition''' between '''compilation''' and '''execution''' '''phase''' of the main program and
* to perform some '''checks''' or '''initialisation''' after compilation and before execution

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| Slide
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| '''UNITCHECK''' and '''CHECK''' blocks runs in '''Last in First out''' manner

whereas

'''INIT''' block runs in '''First In First Out''' manner.

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| Slide

'''UNITCHECK {'''

'''<nowiki># Piece of code to be executed</nowiki>'''

'''}'''
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| The syntax for '''UNITCHECK''' block''' '''is as follows

'''UNITCHECK''' in capital letters space open curly bracket

Press''' Enter'''

Piece of code to be executed

Press''' Enter'''

Close curly bracket

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| Slide

'''CHECK {'''

'''<nowiki># Piece of code to be executed</nowiki>'''

'''}'''
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| The syntax for '''CHECK''' block''' '''is as follows

'''CHECK''' in capital letters space open curly bracket

Press''' Enter'''

Piece of code to be executed

Press''' Enter'''

Close curly bracket

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| Slide

'''INIT {'''

'''<nowiki># Piece of code to be initialised</nowiki>'''

'''}'''
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| The syntax for '''INIT''' block''' '''is as follows

'''INIT''' in capital letters space open curly bracket

Press''' Enter'''

Piece of code to be initialised

Press''' Enter'''

Close curly bracket

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"|
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| For better understanding, I recommend that you experiment with these blocks in your Perl scripts.

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| Slide: Summary
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| Let us summarize.

In this tutorial, we have learnt -

* '''BEGIN '''and''' END '''blocks''' '''in''' details '''and 

* '''Introduction '''to''' UNITCHECK, CHECK '''and''' INIT '''blocks''' ''' 

* using sample program

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| Slide: Assignment
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| Here is assignment for you -

Type the below code inside a PERL script;

'''<nowiki>#!/usr/bin/perl</nowiki>'''

'''END {'''

'''@array = ();'''

'''print "Length of an array inside END block: ", $#array + 1, "\n";'''

'''}'''

'''print "Length of an array: ", $#array + 1, "\n";'''

'''BEGIN {'''

'''@array = (1, 2, 3);'''

'''}'''

execute the script and observe the output.

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| About the Project
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| Watch the video available at the following link.

It summaries the Spoken Tutorial project

If you do not have good bandwidth, you can

download and watch it

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| Spoken Tutorial Workshops
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| The Spoken Tutorial Project Team

* Conducts workshops using spoken tutorials
* Gives certificates to those who pass an online test

For more details, please write to

contact at spoken hyphen tutorial dot org

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| Acknowledgment

http://spoken-tutorial.org\NMEICT-Intro
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| Spoken Tutorial Project is a part of the Talk to a

Teacher project

It is supported by the National Mission on

Education through ICT, MHRD, Government of India.

More information on this Mission is available

spoken hyphen tutorial dot org slash NMEICT hyphen Intro

|-
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"|
| style="border-top:none;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:0.0007in solid #000000;padding:0.0382in;"| Hope you enjoyed this '''Perl''' tutorial.

This is Amol Brahmankar signing off.

Thanks for joining

|}

PERL/C2/Blocks-in-Perl/English - Revision history

PoojaMoolya at 07:32, 17 June 2014

Nancyvarkey at 05:10, 11 April 2014

AmolBrahmankar: Created page with ''''Title Of Script: '''BLOCKS in PERL '''Author:''' Amol Brahmankar '''Keywords:''' BLOCKS in perl video tutorial. {| style="border-spacing:0;" | style="border-top:0.0007in …'

@@ Line 8: / Line 8: @@
 {| style="border-spacing:0;"
-| style="border-top:0.0007in solid #000000;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| <center>'''Visual Clue'''</center>
+| style="border-top:0.0007in solid #000000;border-bottom:0.0007in solid #000000;border-left:0.0007in solid #000000;border-right:none;padding:0.0382in;"| <center>'''Visual Cue'''</center>
 | style="border:0.0007in solid #000000;padding:0.0382in;"| <center>'''Narration'''</center>