Difference between revisions of "PERL/C2/Blocks-in-Perl/English-timed"
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{| border=1 | {| border=1 | ||
| − | + | |'''Time''' | |
| − | + | |''Narration''' | |
|- | |- | ||
| − | | 00 | + | | 00:01 |
|Welcome to the spoken tutorial on ''' BLOCKS''' in Perl. | |Welcome to the spoken tutorial on ''' BLOCKS''' in Perl. | ||
|- | |- | ||
| − | | 00 | + | | 00:06 |
| 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 | + | |00:13 |
|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''' | ||
|- | |- | ||
| − | |00 | + | |00:21 |
| I will also be using the ''' gedit''' Text Editor. | | I will also be using the ''' gedit''' Text Editor. | ||
|- | |- | ||
| − | |00 | + | |00:26 |
|You can use any text editor of your choice. | |You can use any text editor of your choice. | ||
|- | |- | ||
| − | |00 | + | |00:31 |
|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 | + | | 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 | + | | 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. | ||
|- | |- | ||
| − | | 00 | + | | 00:50 |
|''' Perl''' provides 5 special '''blocks.''' | |''' Perl''' provides 5 special '''blocks.''' | ||
|- | |- | ||
| − | |00 | + | |00:53 |
|These '''blocks''' get executed at various stages of a '''Perl''' program. | |These '''blocks''' get executed at various stages of a '''Perl''' program. | ||
|- | |- | ||
| − | |00 | + | |00:59 |
|These blocks are: | |These blocks are: | ||
|- | |- | ||
| − | | 01 | + | | 01:01 |
| '''BEGIN''' | | '''BEGIN''' | ||
|- | |- | ||
| − | |01 | + | |01:02 |
|'''END''' | |'''END''' | ||
|- | |- | ||
| − | |01 | + | |01:03 |
|''' UNITCHECK''' | |''' UNITCHECK''' | ||
|- | |- | ||
| − | | 01 | + | | 01:04 |
| ''' CHECK. ''' | | ''' CHECK. ''' | ||
|- | |- | ||
| − | |01 | + | |01:05 |
|''' INIT ''' | |''' INIT ''' | ||
|- | |- | ||
| − | |01 | + | |01:06 |
| Let us start with understanding the ''' BEGIN''' block. | | Let us start with understanding the ''' BEGIN''' block. | ||
|- | |- | ||
| − | |01 | + | |01:10 |
|''' BEGIN''' block get executed at the time of compilation. | |''' BEGIN''' block get executed at the time of compilation. | ||
|- | |- | ||
| − | |01 | + | |01:15 |
|So, any code written inside this block gets executed first during compilation. | |So, any code written inside this block gets executed first during compilation. | ||
|- | |- | ||
| − | |01 | + | |01:22 |
|We can have several ''' BEGIN ''' blocks inside a ''' Perl''' script. | |We can have several ''' BEGIN ''' blocks inside a ''' Perl''' script. | ||
|- | |- | ||
| − | |01 | + | |01:26 |
| These blocks will get executed in the order of declaration. | | These blocks will get executed in the order of declaration. | ||
|- | |- | ||
| − | | 01 | + | | 01:31 |
|That is in the ''' First define First execute ''' pattern | |That is in the ''' First define First execute ''' pattern | ||
|- | |- | ||
| − | |01 | + | |01:35 |
|The syntax for ''' BEGIN block''' is as follows | |The syntax for ''' BEGIN block''' is as follows | ||
|- | |- | ||
| − | |01 | + | |01:40 |
| '''BEGIN''' in capital letters space open curly bracket | | '''BEGIN''' in capital letters space open curly bracket | ||
|- | |- | ||
| − | | 01 | + | | 01:45 |
| Press ''' Enter.''' | | Press ''' Enter.''' | ||
|- | |- | ||
| − | |01 | + | |01:47 |
|Piece of code to be executed at the time of compilation | |Piece of code to be executed at the time of compilation | ||
|- | |- | ||
| − | |01 | + | |01:51 |
| Press '''Enter ''' | | Press '''Enter ''' | ||
|- | |- | ||
| − | |01 | + | |01:52 |
|Close curly bracket | |Close curly bracket | ||
|- | |- | ||
| − | |01 | + | |01:55 |
|Now, let us look at an example of '''BEGIN''' blocks. | |Now, let us look at an example of '''BEGIN''' blocks. | ||
|- | |- | ||
| − | |01 | + | |01:59 |
|Open the Terminal and type | |Open the Terminal and type | ||
|- | |- | ||
| − | |02 | + | |02:02 |
| ''' gedit beginBlock dot pl ''' space '''ampersand''' | | ''' gedit beginBlock dot pl ''' space '''ampersand''' | ||
|- | |- | ||
| − | |02 | + | |02:08 |
|and press '''Enter.''' | |and press '''Enter.''' | ||
|- | |- | ||
| − | |02 | + | |02:10 |
|This will open the ''' beginBlock dot pl ''' file in '''gedit. ''' | |This will open the ''' beginBlock dot pl ''' file in '''gedit. ''' | ||
|- | |- | ||
| − | |02 | + | |02:15 |
|Type the following piece of code as displayed on the screen. | |Type the following piece of code as displayed on the screen. | ||
|- | |- | ||
| − | |02 | + | |02:20 |
|Let us look at what I have written inside the script. | |Let us look at what I have written inside the script. | ||
|- | |- | ||
| − | |02 | + | |02:24 |
|Here, we have printed some text before and after ''' BEGIN''' blocks. | |Here, we have printed some text before and after ''' BEGIN''' blocks. | ||
|- | |- | ||
| − | | 02 | + | | 02:31 |
| Similarly, I have written one ''' print statement''' in each '''BEGIN''' block. | | Similarly, I have written one ''' print statement''' in each '''BEGIN''' block. | ||
|- | |- | ||
| − | | 02 | + | | 02:37 |
|Please note, I have not given the semicolon after the ''' BEGIN''' blocks. | |Please note, I have not given the semicolon after the ''' BEGIN''' blocks. | ||
|- | |- | ||
| − | | 02 | + | | 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. | ||
|- | |- | ||
| − | |02 | + | |02:49 |
|Now, press ''' Ctrl+s''' to save the file. | |Now, press ''' Ctrl+s''' to save the file. | ||
|- | |- | ||
| − | | 02 | + | | 02:53 |
| Then switch to terminal and execute the script by typing, | | Then switch to terminal and execute the script by typing, | ||
|- | |- | ||
| − | | 02 | + | | 02:58 |
|''' perl beginBlock dot pl''' | |''' perl beginBlock dot pl''' | ||
|- | |- | ||
| − | |03 | + | |03:01 |
|and press '''Enter.''' | |and press '''Enter.''' | ||
|- | |- | ||
| − | |03 | + | |03:04 |
|You will get the output as displayed on the terminal. | |You will get the output as displayed on the terminal. | ||
|- | |- | ||
| − | | 03 | + | | 03:09 |
| 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 | + | |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 | + | | 03:25 |
| '''BEGIN blocks''' gets executed in the order of their declaration. | | '''BEGIN blocks''' gets executed in the order of their declaration. | ||
|- | |- | ||
| − | | 03 | + | | 03:31 |
| From this example, it is evident that: | | From this example, it is evident that: | ||
|- | |- | ||
| − | | 03 | + | | 03:34 |
|The code written inside the ''' BEGIN''' blocks gets executed first. | |The code written inside the ''' BEGIN''' blocks gets executed first. | ||
|- | |- | ||
| − | | 03 | + | | 03:40 |
| This is irrespective of the location of the ''' BEGIN''' block inside ''' PERL''' script. | | This is irrespective of the location of the ''' BEGIN''' block inside ''' PERL''' script. | ||
|- | |- | ||
| − | | 03 | + | | 03:46 |
| '''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 | + | |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 | + | |04:01 |
|Now, let us understand the '''END block ''' | |Now, let us understand the '''END block ''' | ||
|- | |- | ||
| − | |04 | + | |04:04 |
|''' END block''' get executed at the end of PERL program | |''' END block''' get executed at the end of PERL program | ||
|- | |- | ||
| − | |04 | + | |04:09 |
|Code written inside this block gets executed after PERL has finished executing the program. | |Code written inside this block gets executed after PERL has finished executing the program. | ||
|- | |- | ||
| − | |04 | + | |04:17 |
|We can have several ''' END blocks''' inside a '''Perl script.''' | |We can have several ''' END blocks''' inside a '''Perl script.''' | ||
|- | |- | ||
| − | |04 | + | |04:21 |
|These blocks will get executed in reverse order of declaration | |These blocks will get executed in reverse order of declaration | ||
|- | |- | ||
| − | | 04 | + | | 04:26 |
| That is, in '''Last define First execute''' pattern. | | That is, in '''Last define First execute''' pattern. | ||
|- | |- | ||
| − | |04 | + | |04:30 |
|The syntax for ''' END block''' is as follows | |The syntax for ''' END block''' is as follows | ||
|- | |- | ||
| − | |04 | + | |04:35 |
|''' END ''' in capital letters open curly bracket | |''' END ''' in capital letters open curly bracket | ||
|- | |- | ||
| − | |04 | + | |04:39 |
|Press ''' Enter''' | |Press ''' Enter''' | ||
|- | |- | ||
| − | |04 | + | |04:40 |
|Piece of code to be executed at the end of the ''' PERL ''' script | |Piece of code to be executed at the end of the ''' PERL ''' script | ||
|- | |- | ||
| − | |04 | + | |04:45 |
|Press ''' Enter''' | |Press ''' Enter''' | ||
|- | |- | ||
| − | |04 | + | |04:46 |
|Close curly bracket | |Close curly bracket | ||
|- | |- | ||
| − | |04 | + | |04:49 |
|Now let us look at an example of END blocks. | |Now let us look at an example of END blocks. | ||
|- | |- | ||
| − | |04 | + | |04:53 |
|Open the Terminal and type | |Open the Terminal and type | ||
|- | |- | ||
| − | | 04 | + | | 04:56 |
|''' gedit endBlock dot pl space ampersand''' | |''' gedit endBlock dot pl space ampersand''' | ||
|- | |- | ||
| − | | 05 | + | | 05:00 |
|and press '''Enter''' | |and press '''Enter''' | ||
|- | |- | ||
| − | |05 | + | |05:03 |
| This will open the ''' endBlock dot pl''' file in '''gedit.''' | | This will open the ''' endBlock dot pl''' file in '''gedit.''' | ||
|- | |- | ||
| − | | 05 | + | | 05:08 |
| Type the following piece of code as displayed on the screen. | | Type the following piece of code as displayed on the screen. | ||
|- | |- | ||
| − | | 05 | + | | 05:13 |
| Let us look at what I have written inside this script. | | Let us look at what I have written inside this script. | ||
|- | |- | ||
| − | | 05 | + | | 05:17 |
| Here we have printed some text before and after ''' END''' blocks. | | Here we have printed some text before and after ''' END''' blocks. | ||
|- | |- | ||
| − | | 05 | + | | 05:23 |
|Similarly, we have written one print statement in each ''' END''' block. | |Similarly, we have written one print statement in each ''' END''' block. | ||
|- | |- | ||
| − | | 05 | + | | 05:29 |
| Please note, I have not given the ''' semicolon''' after the '''END''' block. | | Please note, I have not given the ''' semicolon''' after the '''END''' block. | ||
|- | |- | ||
| − | |05 | + | |05:34 |
|If we give the semicolon, there will be a syntax error on compilation. | |If we give the semicolon, there will be a syntax error on compilation. | ||
|- | |- | ||
| − | | 05 | + | | 05:41 |
| Now, press ''' Ctrl+s''' to save the file. | | Now, press ''' Ctrl+s''' to save the file. | ||
|- | |- | ||
| − | | 05 | + | | 05:45 |
| Then switch to terminal and execute the script by typing, | | Then switch to terminal and execute the script by typing, | ||
|- | |- | ||
| − | |05 | + | |05:50 |
|''' perl endBlock dot pl''' | |''' perl endBlock dot pl''' | ||
|- | |- | ||
| − | | 05 | + | | 05:53 |
|and '''press Enter.''' | |and '''press Enter.''' | ||
|- | |- | ||
| − | |05 | + | |05:55 |
| You will get the output as displayed on the terminal. | | You will get the output as displayed on the terminal. | ||
|- | |- | ||
| − | |06 | + | |06:00 |
| Notice that : The line written inside the ''' END''' block is printed last. | | Notice that : The line written inside the ''' END''' block is printed last. | ||
|- | |- | ||
| − | | 06 | + | | 06:06 |
| The last ''' print statement''' in the script actually gets printed before the '''END block statements and | | The last ''' print statement''' in the script actually gets printed before the '''END block statements and | ||
|- | |- | ||
| − | | 06 | + | | 06:13 |
| ''' END''' blocks gets executed in the reverse order of their declaration. | | ''' END''' blocks gets executed in the reverse order of their declaration. | ||
|- | |- | ||
| − | | 06 | + | | 06:20 |
| From the example, it is evident that | | From the example, it is evident that | ||
|- | |- | ||
| − | | 06 | + | | 06:23 |
|The code written inside the ''' END''' blocks get executed at the end. | |The code written inside the ''' END''' blocks get executed at the end. | ||
|- | |- | ||
| − | |06 | + | |06:29 |
| This is irrespective of the location of the ''' END''' block inside the '''PERL''' script and | | This is irrespective of the location of the ''' END''' block inside the '''PERL''' script and | ||
|- | |- | ||
| − | |06 | + | |06:36 |
|'''END''' blocks gets executed in the ''' Last In First Out''' manner. | |'''END''' blocks gets executed in the ''' Last In First Out''' manner. | ||
|- | |- | ||
| − | |06 | + | |06:41 |
|So, one use of '''END''' block is to destroy objects created in the program, before exiting. | |So, one use of '''END''' block is to destroy objects created in the program, before exiting. | ||
|- | |- | ||
| − | |06 | + | |06:49 |
| Similarly, ''' PERL''' has ''' UNITCHECK, CHECK''' and ''' INIT''' blocks. | | Similarly, ''' PERL''' has ''' UNITCHECK, CHECK''' and ''' INIT''' blocks. | ||
|- | |- | ||
| − | |06 | + | |06:55 |
|These blocks are used rarely by developers and are a bit difficult to understand. | |These blocks are used rarely by developers and are a bit difficult to understand. | ||
|- | |- | ||
| − | |07 | + | |07:02 |
| So, I will be just briefing you about these blocks. | | So, I will be just briefing you about these blocks. | ||
|- | |- | ||
| − | |07 | + | |07:06 |
|''' UNITCHECK, CHECK''' and '''INIT''' blocks are useful- | |''' UNITCHECK, CHECK''' and '''INIT''' blocks are useful- | ||
|- | |- | ||
| − | |07 | + | |07:10 |
|to catch the transition between compilation and execution phase of the main program and | |to catch the transition between compilation and execution phase of the main program and | ||
|- | |- | ||
| − | |07 | + | |07:18 |
|to perform some checks or initialisation, after compilation and before execution | |to perform some checks or initialisation, after compilation and before execution | ||
|- | |- | ||
| − | |07 | + | |07:24 |
|''' UNITCHECK''' and '''CHECK''' blocks runs in '''Last in First out''' manner | |''' UNITCHECK''' and '''CHECK''' blocks runs in '''Last in First out''' manner | ||
|- | |- | ||
| − | |07 | + | |07:31 |
|whereas '''INIT''' block runs in '''First In First Out''' manner. | |whereas '''INIT''' block runs in '''First In First Out''' manner. | ||
|- | |- | ||
| − | |07 | + | |07:37 |
|The syntax for '''UNITCHECK''' block is as follows | |The syntax for '''UNITCHECK''' block is as follows | ||
|- | |- | ||
| − | |07 | + | |07:41 |
|''' UNITCHECK''' in capital letters space open curly bracket | |''' UNITCHECK''' in capital letters space open curly bracket | ||
|- | |- | ||
| − | |07 | + | |07:46 |
|Press '''Enter''' | |Press '''Enter''' | ||
|- | |- | ||
| − | |07 | + | |07:48 |
|Piece of code to be executed | |Piece of code to be executed | ||
|- | |- | ||
| − | |07 | + | |07:50 |
|Press '''Enter''' | |Press '''Enter''' | ||
|- | |- | ||
| − | |07 | + | |07:52 |
|Close curly bracket | |Close curly bracket | ||
|- | |- | ||
| − | |07 | + | |07:54 |
|The syntax for '''CHECK''' block is as follows | |The syntax for '''CHECK''' block is as follows | ||
|- | |- | ||
| − | |07 | + | |07:58 |
|'''CHECK''' in capital letters space open curly bracket | |'''CHECK''' in capital letters space open curly bracket | ||
|- | |- | ||
| − | |08 | + | |08:03 |
|Press '''Enter''' | |Press '''Enter''' | ||
|- | |- | ||
| − | |08 | + | |08:04 |
|Piece of code to be executed | |Piece of code to be executed | ||
|- | |- | ||
| − | |08 | + | |08:07 |
|Press '''Enter ''' | |Press '''Enter ''' | ||
|- | |- | ||
| − | |08 | + | |08:08 |
|Close curly bracket | |Close curly bracket | ||
|- | |- | ||
| − | |08 | + | |08:11 |
|The syntax for '''INIT''' block is as follows | |The syntax for '''INIT''' block is as follows | ||
|- | |- | ||
| − | |08 | + | |08:15 |
|''' INIT''' in capital letters space open curly bracket | |''' INIT''' in capital letters space open curly bracket | ||
|- | |- | ||
| − | |08 | + | |08:20 |
|Press '''Enter ''' | |Press '''Enter ''' | ||
|- | |- | ||
| − | |08 | + | |08:21 |
|Piece of code to be initialised | |Piece of code to be initialised | ||
|- | |- | ||
| − | |08 | + | |08:24 |
|Press '''Enter ''' | |Press '''Enter ''' | ||
|- | |- | ||
| − | |08 | + | |08:26 |
|Close curly bracket | |Close curly bracket | ||
|- | |- | ||
| − | |08 | + | |08:28 |
|For better understanding, I recommend that you experiment with these blocks in your '''Perl''' scripts. | |For better understanding, I recommend that you experiment with these blocks in your '''Perl''' scripts. | ||
|- | |- | ||
| − | |08 | + | |08:36 |
|Let us summarize. | |Let us summarize. | ||
|- | |- | ||
| − | |08 | + | |08:37 |
|In this tutorial, we have learnt - | |In this tutorial, we have learnt - | ||
|- | |- | ||
| − | |08 | + | |08:40 |
|''' BEGIN''' and '''END''' blocks in detail and | |''' BEGIN''' and '''END''' blocks in detail and | ||
|- | |- | ||
| − | |08 | + | |08:44 |
|Introduction to ''' UNITCHECK, CHECK''' and '''INIT ''' blocks | |Introduction to ''' UNITCHECK, CHECK''' and '''INIT ''' blocks | ||
|- | |- | ||
| − | |08 | + | |08:48 |
|using sample programs | |using sample programs | ||
|- | |- | ||
| − | |08 | + | |08:52 |
|Here is assignment for you - | |Here is assignment for you - | ||
|- | |- | ||
| − | |08 | + | |08:54 |
|Type the below code inside a PERL script; | |Type the below code inside a PERL script; | ||
|- | |- | ||
| − | |08 | + | |08:58 |
|Execute the script and observe the output. | |Execute the script and observe the output. | ||
|- | |- | ||
| − | |09 | + | |09:02 |
|Watch the video available at the following link | |Watch the video available at the following link | ||
|- | |- | ||
| − | |09 | + | |09:06 |
|It summaries the Spoken Tutorial project | |It summaries the Spoken Tutorial project | ||
|- | |- | ||
| − | |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 | + | | 09:14 |
| The Spoken Tutorial Project Team Conducts workshops using spoken tutorials | | The Spoken Tutorial Project Team Conducts workshops using spoken tutorials | ||
|- | |- | ||
| − | |09 | + | |09:20 |
|Gives certificates to those who pass an online test | |Gives certificates to those who pass an online test | ||
|- | |- | ||
| − | |09 | + | |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 | + | | 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 | ||
|- | |- | ||
| − | |09 | + | |09:37 |
|It is supported by the National Mission on Education through ICT, MHRD, Government of India. | |It is supported by the National Mission on Education through ICT, MHRD, Government of India. | ||
|- | |- | ||
| − | |09 | + | |09:45 |
|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 | ||
|- | |- | ||
| − | | 09 | + | | 09:57 |
| Hope you enjoyed this Perl tutorial. | | Hope you enjoyed this Perl tutorial. | ||
|- | |- | ||
| − | |10 | + | |10:00 |
|This is Amol signing off. | |This is Amol signing off. | ||
|- | |- | ||
| − | |10 | + | |10:02 |
|Thanks for joining. | |Thanks for joining. | ||
|} | |} | ||
Revision as of 11:53, 10 July 2014
| 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 get 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 blocks. |
| 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 gets 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 get 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 initialised |
| 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 summaries 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. |
