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

|Welcome to the spoken tutorial on ''' BLOCKS''' in Perl.  

| In this tutorial, we will learn about the various ''' BLOCKS''' available in '''Perl'''

|I am using ''' Ubuntu Linux 12.04''' operating system and ''' Perl 5.14.2'''

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

|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.  

|''' Perl''' provides 5 special '''blocks.'''  

| '''BEGIN'''  

   

|'''END'''  

|''' UNITCHECK'''

 

| ''' CHECK. '''

|''' INIT '''

 

| Let us start with understanding the ''' BEGIN''' block.   

|''' BEGIN''' block get executed at the time of compilation.  

|That is in the ''' First define First execute ''' pattern  

|The syntax for ''' BEGIN block''' is as follows  

|Piece of code to be executed at the time of compilation  

| Press '''Enter '''

 

|Close curly bracket  

|Now, let us look at an example of '''BEGIN''' blocks.  

|Open the Terminal and type  

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

|Here, we have printed some text before and after ''' BEGIN''' blocks.  

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

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

|Now, press ''' Ctrl+s''' to save the file.  

| Then switch to  terminal and execute the script by typing,

| 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.  

|   03:31

|  From this example, it is evident that:

|The code written inside the ''' BEGIN'''  blocks gets 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.  

|Now, let us understand the '''END block '''

|''' END block''' get executed at the end of PERL program  

|We can have several ''' END blocks'''  inside a '''Perl script.'''  

|These blocks will get executed in reverse order of declaration  

|The syntax for ''' END block''' is as follows  

|Press ''' Enter'''  

 

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

|Press ''' Enter'''

 

|Close curly bracket  

|Now let us look at an example of END blocks.  

|Open the Terminal and type  

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

|and press '''Enter'''

| Here we have printed some text before and after ''' 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.  

| Now, press ''' Ctrl+s''' to save the file.  

| Then switch to terminal and execute the script by typing,

|and '''press Enter.'''

| 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.  

|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.  

| Similarly, ''' PERL''' has ''' UNITCHECK, CHECK''' and ''' INIT''' blocks.  

|''' UNITCHECK, CHECK''' and '''INIT''' blocks are useful-

|to perform some checks or initialisation, after compilation and before execution  

|''' UNITCHECK''' and '''CHECK''' blocks runs in '''Last in First out''' manner   

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

|The syntax for '''UNITCHECK''' block is as follows  

|Press '''Enter'''  

|Piece of code to be executed  

|Press '''Enter'''

|Close curly bracket  

|The syntax for '''CHECK''' block is as follows

|Press '''Enter'''  

 

|Piece of code to be executed  

|Press '''Enter '''

 

|Close curly bracket  

|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  

|Let us summarize.  

 

|In this tutorial, we have learnt -

|''' BEGIN''' and '''END''' blocks in detail and  

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

|using sample programs  

|Here is assignment for you -

|Type the below code inside a PERL script;  

|Execute the script and observe the output.  

|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

|  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

|  Spoken Tutorial Project is a part of the Talk to a Teacher project

|More information on this Mission is available at spoken hyphen tutorial dot org slash NMEICT hyphen Intro

| Hope you enjoyed this Perl tutorial.  

|This is Amol signing off.