PoojaMoolya at 12:47, 20 February 2017

2017-02-20T12:47:42Z

Sandhya.np14 at 11:50, 16 February 2016

2016-02-16T11:50:41Z

Sandhya.np14 at 07:09, 16 February 2016

2016-02-16T07:09:35Z

Sandhya.np14 at 16:51, 28 December 2015

2015-12-28T16:51:57Z

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PoojaMoolya: Created page with " {| Border = 1 | '''Time''' | '''Narration''' |- | 00:01 | Welcome to the''' Spoken Tutorial''' on''' Exception and error handling in PERL..."

2015-11-24T07:29:01Z

Created page with " {| Border = 1 | <center>'''Time'''</center> | <center>'''Narration'''</center> |- | 00:01 | Welcome to the''' Spoken Tutorial''' on''' Exception and error handling in PERL..."

New page

{| Border = 1
| <center>'''Time'''</center>
| <center>'''Narration'''</center>

|-
| 00:01
| Welcome to the''' Spoken Tutorial''' on''' Exception and error handling in PERL'''

|-
| 00:06
| In this tutorial we will learn to

* Catch errors and
* Handle exceptions
|-
| 00:12
| For this tutorial, I am using

* '''Ubuntu Linux 12.04''' operating system
* '''Perl 5.14.2'''
* and the''' gedit''' Text Editor

|-
| 00:23
|You can use any text editor of your choice.

|-
| 00:27
| To follow this tutorial, you should have working knowledge of''' Perl''' Programming.

|-
| 00:32
|If not, then go through the relevant''' Perl''' spoken tutorials on the''' spoken tutorial''' website.

|-
|00:39
| When an error occurs: '''Exception handling''' deviates the execution of a program from the normal execution path.

|-
| 00:47
| '''Error handling''' helps to recover the program, without terminating the application.

|-
| 00:53
| We can identify and trap an error in a number of ways. We will see few commonly used methods in '''Perl'''.

|-
| 01:01
| The''' warn''' function only raises a warning message without taking further action.
|-
| 01:07
| The''' die''' function immediately terminates the execution and displays the error message.

|-
| 01:13
| Let us understand the''' die''' function using a sample program, which I have already saved.

|-
| 01:20
| Go to the''' terminal''' and type '''gedit die dot pl ampersand '''and press''' Enter'''

|-
|01:29
| This is code in''' die.pl''' file. Let us understand the code now.

|-
|01:35
| Here we have defined a '''function divide''' which takes two '''input parameters'''

i.e '''dollar numerator '''and''' dollar''' '''denominator'''

|-
| 01:46
|'''At the rate underscore '''(@_) is a '''special variable '''used to pass the '''parameter list''' to the '''function'''.

|-
| 01:53
| If the '''denominator''' is zero, the '''die''' function will quit the script.

|-
| 01:57
|It will also display the error message for the user to read.

Else it will print the output.

|-
| 02:05
| These are the '''function call statements'''.

|-
| 02:08
|The first two times, the '''function''' is executed because the '''second parameter''' is not zero.

|-
| 02:15
| The third time, the '''denominator''' value is zero, so the '''die function''' is executed.

|-
| 02:23

| The last '''divide function '''will not be executed as the '''die function '''quits the script.

|-
| 02:29
| Press''' Ctrl + S''' to save the program.

|-
| 02:32
| Let us execute the program.

|-
| 02:35
| Switch back to the''' terminal''' and type, '''perl die dot pl''' and press''' Enter'''.

|-
|02:43
| The output is displayed as shown here.

'''Can't divide by zero! -'''

|-
| 02:49
|This is the error message we have given in the program in the '''die''' statement.

|-
| 02:54
| Next, we will see how to use''' eval function '''in error handling.

|-
| 03:00
| '''eval function '''is used for handling run-time errors or exceptions.

|-
| 03:06
|For example, built-in errors such as '''out of memory, divide by zero''' or user defined errors.

|-
| 03:14
| The general syntax for''' eval function''' is shown here.

|-
| 03:19
|The''' dollar exclamation'''('''$!) '''special variable holds the error message, if any.

|-
| 03:25
|Otherwise, '''dollar exclamation( $!) '''holds an empty string. That means it is evaluated as '''false'''.

|-
| 03:33
| Let us understand the''' eval''' function using a sample program.
Go to the''' terminal.'''
|-
| 03:40
| Type '''gedit eval dot pl ampersand '''and press''' Enter'''

|-
| 03:47
| In the''' eval dot pl''' file, type the following code as displayed on the screen.
Let me explain the code now.

|-
| 03:54
| Here in our example,'''open FILE''' invokes the''' die statement, '''if it has trouble in opening a file''' “test.dat”'''

|-
| 04:05
| '''Perl''' gives the '''system error message''' from the last '''eval''' block to the variable '''dollar exclamation( $!)'''

|-
| 04:13
| Press '''Ctrl + S''' to save the file.

|-
| 04:17
| Switch back to the''' terminal''' and type, '''perl eval dot pl''' and press''' Enter'''.

|-
| 04:25
| The '''system error message''' is displayed as shown here.

|-
| 04:30
| Let us see another example. This time we will see an error message returned from '''eval''' function using '''$@''' '''(dollar at the rate).'''

|-
| 04:40
| Let us switch back to the '''eval dot pl''' file.

|-
| 04:44
| Type the code as shown on the screen.

|-
| 04:48
|We are passing''' $total''', '''$count''' as input parameters to the '''function average'''.

|-
| 04:56
|We have a possibility of getting an error if the count is zero.

|-
| 05:00
|Here, that is handled with the '''die statement'''.

|-
| 05:04
|The error message returned from '''eval''' is displayed using '''$@ ( dollar at the rate)'''

|-
| 05:11
|If not, it will print the '''Average''' value.

|-
| 05:15
| Press Ctrl +S to save the file. Let us execute the program.

|-
| 05:22
| Switch back to the''' terminal''' and type, '''perl eval.pl''' and press''' Enter'''.

|-
| 05:31
| The output is as shown here.

|-
| 05:35
| This brings us to the end of this tutorial. Let us summarise.

|-
| 05:41
|In this tutorial, we have learnt how to

* Catch errors and
* Handle exceptions
|-
| 05:47
| As an assignment do the following.

On your '''Linux''' machine, create a file '''emp.txt''' with 5 employee names.

|-
| 05:57
|Change permission of '''emp.txt '''to '''READ''' only.

|-
| 06:02
|'''Note''': Go through the relevant''' Linux''' spoken tutorials on the''' spoken tutorial''' website for '''change permission''' option.

|-
| 06:10
|Write a '''Perl''' program to open the '''emp.txt''' file in '''WRITE''' mode and add few employee names to it.

|-
| 06:19
| Using "'''eval'''", print appropriate error message if '''open/write''' operation fails.

|-
|06:26
| The video at the following link summarises the Spoken Tutorial project.
Please download and watch it.

|-
| 06:33
| The''' Spoken Tutorial Project''' Team

* conducts workshops using spoken tutorials and
* gives certificates on passing online tests.

|-
| 06:42
|For more details, please write to us.
|-
| 06:46
| Spoken Tutorial project is funded by NMEICT, MHRD, Government of India.

|-
| 06:53
|More information on this mission is available at this link.

|-
| 06:58
| This is Nirmala Venkat from IIT Bombay, signing off. Thanks for watching.

|}

@@ Line 11: / Line 11: @@
 | 00:06
 | In this tutorial, we will learn to:
-* '''Catch''' errors and
+'''Catch''' errors and
-* Handle '''exception'''s.
+Handle '''exceptions'''.
 |-
 | 00:12
 | For this tutorial, I am using:
-* '''Ubuntu Linux 12.04''' operating system
+'''Ubuntu Linux 12.04''' operating system
-* '''Perl 5.14.2''' and the
+'''Perl 5.14.2''' and the
-* ''' gedit''' Text Editor.
+''' gedit''' Text Editor.
 |-
@@ Line 152: / Line 152: @@
 |-
 | 03:47
-| In the''' eval dot pl''' file, type the following code as displayed on the screen.
+| In the''' eval dot pl''' file, type the following code as displayed on the screen. Let me explain the code now.
 Let me explain the code now.
 |-
@@ Line 226: / Line 225: @@
 | 05:41
 |In this tutorial, we have learnt how to:
-* Catch errors and
+Catch errors and
-* Handle exceptions.
+Handle exceptions.
 |-
 | 05:47
@@ Line 256: / Line 255: @@
 | 06:33
 | The''' Spoken Tutorial Project''' team:
-* conducts workshops using spoken tutorials and
+conducts workshops using spoken tutorials and
-* gives certificates on passing online tests.
+gives certificates on passing online tests.
 |-

@@ Line 90: / Line 90: @@
 |-
 | 02:15
-| The third time, the '''denominator''' value is zero, so the '''die''' function is executed.
+| The third time, the '''denominator''' value is zero. So, the '''die''' function is executed.
 |-
@@ Line 116: / Line 116: @@
 |-
 | 02:49
-|This is the error message we have given in the program in the '''die''' statement.
+|This is the error message we have given in the program, in the '''die''' statement.
 |-

@@ Line 173: / Line 173: @@
 |-
 | 04:25
-| The '''system error message''' is displayed as shown here.
+| The system error message is displayed as shown here.
 |-
 | 04:30
-| Let us see another example. This time we will see an error message returned from '''eval''' function using '$@' ('''dollar at the rate''').
+| Let us see another example. This time, we will see an error message returned from '''eval''' function using '$@' ('''dollar at the rate''').
 |-

PERL/C3/Exception-and-error-handling-in-PERL/English-timed - Revision history

PoojaMoolya at 12:47, 20 February 2017

Sandhya.np14 at 11:50, 16 February 2016

Sandhya.np14 at 07:09, 16 February 2016

Sandhya.np14 at 16:51, 28 December 2015

PoojaMoolya: Created page with " {| Border = 1 | '''Time''' | '''Narration''' |- | 00:01 | Welcome to the''' Spoken Tutorial''' on''' Exception and error handling in PERL..."