PERL/C3/Special-Variables-in-PERL/English - Revision history

Nancyvarkey at 12:35, 14 July 2015

2015-07-14T12:35:44Z

Nancyvarkey at 12:19, 14 July 2015

2015-07-14T12:19:38Z

Nirmala Venkat at 11:49, 13 July 2015

2015-07-13T11:49:08Z

Nirmala Venkat at 11:48, 13 July 2015

2015-07-13T11:48:11Z

Nirmala Venkat: Created page with "'''Title of script''':''' Special Variables in PERL''' '''Author: Nirmala Venkat''' '''Keywords: Special Variables, Global special variables, Special command line variables, G..."

2015-07-13T11:46:59Z

Created page with "'''Title of script''':''' Special Variables in PERL''' '''Author: Nirmala Venkat''' '''Keywords: Special Variables, Global special variables, Special command line variables, G..."

New page

'''Title of script''':''' Special Variables in PERL'''
'''Author: Nirmala Venkat'''
'''Keywords: Special Variables, Global special variables, Special command line variables, Global special constants''', '''gedit''', '''video tutorial'''
{| style="border-spacing:0;"
| style="background-color:#c0c0c0;border:1pt solid #000000;padding:0.097cm;"| <center>'''Visual Cue'''</center>
| style="background-color:#c0c0c0;border:1pt solid #000000;padding:0.097cm;"| <center>'''Narration'''</center>
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Slide 1:
| style="border:1pt solid #000000;padding:0.097cm;"| Welcome to the''' Spoken Tutorial''' on''' special variables '''in '''Perl.'''
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Slide 2:
Learning objectives
| style="border:1pt solid #000000;padding:0.097cm;"| In this tutorial we will learn about
* Global special variables
* Special command line variables
* Global special constants
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Slide 3:
System Requirements
| style="border:1pt solid #000000;padding:0.097cm;"| For this tutorial, I am using
* '''Ubuntu Linux 12.04''' operating system
* '''Perl 5.14.2'''
* and the''' gedit''' Text Editor
You can use any text editor of your choice.
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Slide 4:
Pre-requisites
| style="border:1pt solid #000000;padding:0.097cm;"| As a prerequisite, you should have working knowledge of '''Perl''' Programming.

If not, then go through the relevant''' Perl''' spoken tutorials on the''' spoken tutorial''' website.
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Slide 5:
| style="border:1pt solid #000000;padding:0.097cm;"| What are''' special variables'''?
'''Special variables''' are predefined variables that have a special meaning in '''Perl'''.

These do not need to be initialised before use.

These are used to hold the results of searches, '''environment variables''' and '''flags''' to control '''debugging'''.
|-
| style="border:1pt solid #000000;padding:0.097cm;"|
| style="border:1pt solid #000000;padding:0.097cm;"| First, we will learn about''' Global special variables.'''
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Slide 6:
| style="border:1pt solid #000000;padding:0.097cm;"| '''$_ : (Dollar Underscore)'''
This is a widely used''' special variable'''.

'''$_''' - '''Dollar Underscore '''is the default parameter for lot of functions and pattern-searching strings.
|-
| style="border:1pt solid #000000;padding:0.097cm;"|
| style="border:1pt solid #000000;padding:0.097cm;"| Let us understand the usage of '''$_ variable''' using a sample program.
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Switch to the Terminal and type
'''gedit special.pl''' &
| style="border:1pt solid #000000;padding:0.097cm;"| I will open the''' special dot pl file''' which i have already created.

Go to the terminal and type''' gedit special.pl ampersand '''and press '''Enter.'''
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Point the cursor''' special.pl'''
| style="border:1pt solid #000000;padding:0.097cm;"| '''special.pl''' file is now open in '''gedit Text Editor'''.
Type the code as displayed on the screen.

Let me explain the code now.
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Highlight in gedit

'''<nowiki>#Example1</nowiki>'''

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

'''foreach my $color ('Red','Green','Blue') {'''

'''print “$color \n”;'''
'''}'''

'''foreach ('Red','Green','Blue') {'''

'''print “$_ \n”;'''
'''}'''
| style="border:1pt solid #000000;padding:0.097cm;"| There are 2 '''foreach '''loops here.

Both these''' foreach''' loops will execute the same result.

In each iteration of the loop, the current string is placed in '''$_'''.

And it is used by the '''print statement, '''by default.

'''$_ '''saves the use of one extra variable '''$color'''.
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Press''' Ctrl+S'''
| style="border:1pt solid #000000;padding:0.097cm;"| Press''' Ctrl+S''' to save the file.

Then switch to the''' terminal''' and execute the '''Perl''' script by typing

'''perl special dot pl''' and press''' Enter'''.

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Highlight the output
| style="border:1pt solid #000000;padding:0.097cm;"| Here both '''foreach''' loops gives the same output.
|-
| style="border:1pt solid #000000;padding:0.097cm;"|
| style="border:1pt solid #000000;padding:0.097cm;"| Now, let us see another example to demonstrate how '''$_ variable '''is '''implicit'''.

Go back to the '''special dot pl file'''.
|-
| style="border:1pt solid #000000;padding:0.097cm;"| '''<nowiki>#Example2</nowiki>'''

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

'''<nowiki>open(DATA, "<first.txt") or die "Couldn't open file first.txt, $!";</nowiki>'''

'''<nowiki>while(<DATA>){</nowiki>'''

'''print "$_";'''
'''}'''
| style="border:1pt solid #000000;padding:0.097cm;"| Type the piece of code shown on the screen.

This program reads a '''text file first.txt '''line by line.

Then it loops through the '''DATA''' file, till all lines are read.

'''print $_ '''variable prints the contents of the current line from the''' first.txt''' file.

In the ''''while'''' loop, the use of '''$_''' is '''implicit.'''
|-
| style="border:1pt solid #000000;padding:0.097cm;"|
| style="border:1pt solid #000000;padding:0.097cm;"| We will see more about this in future tutorials.
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Slide: 7
| style="border:1pt solid #000000;padding:0.097cm;"| '''At the rate underscore''' is the '''special variable''' used to store '''subroutine parameters.'''

'''Arguments''' for a '''subroutine''' are stored in this array variable.

'''Array operations''' like '''pop/shift '''can be done on this '''variable''' as we do in normal '''arrays'''.
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Switch to the Terminal and type
'''gedit special.pl''' &
| style="border:1pt solid #000000;padding:0.097cm;"| I will show an example for this.

Let us switch back to '''special dot pl file''' once again.
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Point the cursor''' special.pl'''
| style="border:1pt solid #000000;padding:0.097cm;"| Type the code as displayed on the screen.
|-
| style="border:1pt solid #000000;padding:0.097cm;"| '''sub max {'''
'''my ($a, $b) = @_;'''

'''if ($a > $b) {'''

'''return $a;'''

'''}'''

'''return $b;'''

'''}'''

'''print max(23, 42);'''
| style="border:1pt solid #000000;padding:0.097cm;"| This program will return the '''maximum value '''between two numbers.
'''@_ - At the rate underscore''' is a '''local array '''which stores the two '''arguments dollar a comma dollar b.'''

That is, it is stored under
* dollar underscore index of zero
* and dollar underscore index of one
* i.e '''<nowiki>$_[0] </nowiki>'''and '''<nowiki>$_[1]</nowiki>'''

The '''print statement '''prints the '''maximum '''of the two given numbers.
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Press''' Ctrl+S'''
| style="border:1pt solid #000000;padding:0.097cm;"| Press''' Ctrl+S''' to save the file.

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Switch to terminal
'''perl special dot pl'''
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Switch to the''' terminal''' and execute the '''Perl '''script by typing
'''perl special dot pl''' and press''' Enter'''.
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Highlight the output
| style="border:1pt solid #000000;padding:0.097cm;"| The maximum value is displayed as output.

Let’s move on.
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Slide:8
| style="border:1pt solid #000000;padding:0.097cm;"| '''Environment variables '''are represented by '''percentage '''followed by '''capital ENV'''.

'''Environment variables '''contain a copy of the current '''environment variables, '''such as the following.
* '''PWD, USER, LANG, PATH,''' etc.
|-
| style="border:1pt solid #000000;padding:0.097cm;"|
| style="border:1pt solid #000000;padding:0.097cm;"| Let us understand''' %ENV''' variable using a sample program.
|-
| style="border:1pt solid #000000;padding:0.097cm;"|
| style="border:1pt solid #000000;padding:0.097cm;"| We will switch back to the''' special dot pl file'''.
|-
| style="border:1pt solid #000000;padding:0.097cm;"| '''Example''':
'''foreach (keys %ENV) {'''

'''print $_, "::", $ENV{$_}, "\n";'''

'''}'''
| style="border:1pt solid #000000;padding:0.097cm;"| Type the following code as displayed on the screen.
|-
| style="border:1pt solid #000000;padding:0.097cm;"|
| style="border:1pt solid #000000;padding:0.097cm;"| Press''' Ctrl+S''' to save the file.
Switch to the''' terminal''' and execute the '''Perl '''script.
Type''' perl special dot pl''' and press''' Enter'''.
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Highlight the output
| style="border:1pt solid #000000;padding:0.097cm;"| We can see the current environment details such as
* '''PWD (present working directory)''', username, language etc.
|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"|
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Next we will see about another '''special variable''' '''dollar zero'''
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Slide:9
'''Example:'''

'''print $0, "\n";'''
| style="border:1pt solid #000000;padding:0.097cm;"| The '''special variable dollar zero''' ('''$0''') contains name of the current '''Perl '''program that is being executed.

This is generally used for logging purpose.

For example:
I have a file named '''First.pl '''within which I am using '''$0 '''variable''' '''as shown here.

On executing, it will print the filename '''First.pl'''.
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Slide:10
| style="border:1pt solid #000000;padding:0.097cm;"| '''Perl''' has a''' built-in function''' called '''sort''' that sorts an '''array'''.

A '''comparison function''' will compare its parameters using the''' numerical comparison operator.'''

This operator is represented by''' lesser than equal to greater than symbols, '''as shown here.
|-
| style="border:1pt solid #000000;padding:0.097cm;"|
| style="border:1pt solid #000000;padding:0.097cm;"| Let us see an example for this.
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Switch to the Terminal and type
'''gedit sort.pl''' &
| style="border:1pt solid #000000;padding:0.097cm;"| Open the '''terminal''' and type''' '''
'''gedit sort.pl ampersand '''and press''' Enter.'''
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Point the cursor''' sort.pl'''
| style="border:1pt solid #000000;padding:0.097cm;"| '''sort.pl''' file is now open in '''gedit Text Editor'''.

Type the following code as displayed on the screen.
|-
| style="border:1pt solid #000000;padding:0.097cm;"| '''<nowiki>#!/usr/bin/perl</nowiki>'''

'''<nowiki># sort numerically ascending</nowiki>'''

'''my @numbers = (14, 6, 12, 3, 28);'''

'''<nowiki>my @sorted_numbers = sort {$a<=>$b} @numbers;</nowiki>'''

'''print @sorted_numbers;'''

| style="border:1pt solid #000000;padding:0.097cm;"| Let me explain the code.
The first line declares an '''array '''of numbers.

The '''numerical comparison operator '''will compare the two values as numbers.

'''Dollar a '''and '''dollar''' '''b '''are '''special package local variables''' in which the values to be compared are loaded.

And this '''sort''' function will sort the numbers in ascending order.
|-
| style="border:1pt solid #000000;padding:0.097cm;"|
| style="border:1pt solid #000000;padding:0.097cm;"| Let us now save and execute the program.
|-
| style="border:1pt solid #000000;padding:0.097cm;"|
| style="border:1pt solid #000000;padding:0.097cm;"| Switch back to the '''terminal''' and type,
'''perl sort.pl''' and press''' Enter'''.
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Highlight
'''Output'''
| style="border:1pt solid #000000;padding:0.097cm;"| We can see that the numbers are sorted in ascending order.
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Slide: 11
'''Example:'''

'''<nowiki>open FH, "<", "hello.txt" or die "Cannot open file for reading : $!";</nowiki>'''
| style="border:1pt solid #000000;padding:0.097cm;"| Let’s see another special variable '''dollar exclamation.'''

'''dollar exclamation''' if used in '''string '''context, returns the '''system error string.'''
Here is an example of its usage.

If the file '''hello.txt '''doesn't exist, it will print the error message,like:

'''Cannot open file for reading : No such file or directory at main.pl line 3.'''
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Slide: 12
'''Example:'''

'''my $result= eval { $x/ $y };'''

'''print “ could not divide $@" if $@;'''

| style="border:1pt solid #000000;padding:0.097cm;"| Let’s now look at another '''special variable''' namely, '''dollar at the rate.'''

This is another widely used '''variable'''.

It returns an error message, returned from''' eval''' or''' require''' command.

This example will print:
'''could not divide Illegal division by zero. '''
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Slide:13
'''Example:'''

'''print “$$\n”;'''

| style="border:1pt solid #000000;padding:0.097cm;"| '''dollar dollar''' is yet another '''special variable.'''

This holds the '''process ID''' of the '''Perl interpreter''' running this script.
|-
| style="border:1pt solid #000000;padding:0.097cm;"|'''Special command line variables'''
| style="border:1pt solid #000000;padding:0.097cm;"|PAUSE

|-
| style="border:1pt solid #000000;padding:0.097cm;"| Slide:14
'''Example:'''

'''<nowiki>while(<>) {</nowiki>'''

'''print "$_ \n";'''
'''}'''
| style="border:1pt solid #000000;padding:0.097cm;"| The '''diamond operator''' is used to read every line, from the files specified on the '''command line'''.
|-
| style="border:1pt solid #000000;padding:0.097cm;"|
| style="border:1pt solid #000000;padding:0.097cm;"| Let us see an example for this.
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Switch to the Terminal and type
'''gedit commandline.pl''' &
| style="border:1pt solid #000000;padding:0.097cm;"| Open the '''terminal''' and type''' gedit commandline.pl ampersand '''and press''' Enter.'''
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Point the cursor''' commandline.pl'''
| style="border:1pt solid #000000;padding:0.097cm;"| '''commandline.pl''' file is now open in '''gedit'''.
|-
| style="border:1pt solid #000000;padding:0.097cm;"|
| style="border:1pt solid #000000;padding:0.097cm;"| Type the code as displayed on the screen.
|-
| style="border:1pt solid #000000;padding:0.097cm;"|
| style="border:1pt solid #000000;padding:0.097cm;"| Save the file.
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Switch to '''sample.txt''' in gedit itself.
| style="border:1pt solid #000000;padding:0.097cm;"| Let me show you the text that I have in a file named '''sample.txt'''
|-
| style="border:1pt solid #000000;padding:0.097cm;"| On the terminal type
'''perl commandline.pl sample.txt'''
| style="border:1pt solid #000000;padding:0.097cm;"| Now, run the program from the '''command line '''by typing: '''perl commandline.pl space sample.txt '''and press''' Enter.'''
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Highlight the output
| style="border:1pt solid #000000;padding:0.097cm;"| This is the text we had in '''sample.txt''' file.

Note: If no files are specified, it reads from the '''STDIN''' (standard input). That is from the keyboard.
<nowiki><<</nowiki>PAUSE>>
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Slide: 15
'''Example:'''

foreach (@ARGV) {

print;

print "\n";
}
| style="border:1pt solid #000000;padding:0.097cm;"| '''Perl''' has an '''array''' '''at the rate capital A R G V '''special variable.
This holds all the values from the '''command line'''.
When using '''array''' '''at the rate capital A R G V, '''there is no need to declare the '''variables.'''

The values from the '''command line''' are automatically placed in this '''variable'''.
|-
| style="border:1pt solid #000000;padding:0.097cm;"| '''Global Special Constants'''
| style="border:1pt solid #000000;padding:0.097cm;"| Let’s now move on to '''Global Special Constants.'''
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Slide:16
| style="border:1pt solid #000000;padding:0.097cm;"| '''underscore underscore E N D ('''in capital letters)'''underscore underscore.'''

…. indicates the logical end of the program.

Any text following this '''special variable '''is ignored after this statement.
|-
| style="border:1pt solid #000000;padding:0.097cm;"|
| style="border:1pt solid #000000;padding:0.097cm;"| '''underscore underscore FILE '''(in capital letters)''' underscore underscore.'''

...represents the filename of the program at the point where it is used.
|-
| style="border:1pt solid #000000;padding:0.097cm;"|
| style="border:1pt solid #000000;padding:0.097cm;"| '''underscore underscore LINE '''(in capital letters) '''underscore underscore.'''

...represents the current line number
|-
| style="border:1pt solid #000000;padding:0.097cm;"|
| style="border:1pt solid #000000;padding:0.097cm;"| '''underscore underscore PACKAGE '''(in capital letters) '''underscore underscore.'''

...represents the current package name at compile time, or undefined if there is no current package.
|-
| style="border:1pt solid #000000;padding:0.097cm;"|
| style="border:1pt solid #000000;padding:0.097cm;"| We will see a sample program on how '''Global Special Constants '''are used.
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Switch to the Terminal and type
'''gedit specialconstant.pl''' &
| style="border:1pt solid #000000;padding:0.097cm;"| Open the '''terminal''' and type''' '''
'''gedit specialconstant.pl ampersand '''
and press '''Enter.'''
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Point the cursor''' specialconstant.pl'''
| style="border:1pt solid #000000;padding:0.097cm;"| '''specialconstant.pl''' file is now open in '''gedit'''.

Type the following code as displayed on the screen.

Let me explain the code now.
|-
| style="border:1pt solid #000000;padding:0.097cm;"| '''<nowiki>#!/usr/bin/perl</nowiki>'''

'''<nowiki># This is second package</nowiki>'''

'''package second;'''

'''our $i = 20;'''

'''print "Package Name : " , __PACKAGE__ , " $i\n"; #print 20'''

'''Print “File name:”, __FILE__, “Line No:”, __LINE__, “\n”;'''

| style="border:1pt solid #000000;padding:0.097cm;"| The '''special literals __PACKAGE__ , __FILE__, __LINE__''' represent the

* package name,
* current filename and
* line number

respectively at that point in the program.
|-
| style="border:1pt solid #000000;padding:0.097cm;"|
| style="border:1pt solid #000000;padding:0.097cm;"| Let us execute the program.
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Switch to the Terminal and type
'''perl specialconstant.pl'''
| style="border:1pt solid #000000;padding:0.097cm;"| Switch back to the '''terminal '''and type:
'''perl specialconstant.pl''' and press''' Enter'''.
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Highlight the output
| style="border:1pt solid #000000;padding:0.097cm;"| We can see the current package name, filename and line number of our program.
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Slide 17:
Summary
| style="border:1pt solid #000000;padding:0.097cm;"| This brings us to the end of this tutorial. Let us summarise.

In this tutorial, we learnt about some commonly used '''special variables''' in '''Perl'''.
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Slide 18:
Assignment
| style="border:1pt solid #000000;padding:0.097cm;"| As an assignment do the following.
Write a '''Perl''' script to sort the following array of numbers in ascending and descending order.

# '''my @numbers = ( 22, 88, 33, 55, 11);'''
# Note: For descending order, use the below code for comparison.
'''sort {$b<nowiki><=>$</nowiki>a} @numbers<nowiki>;</nowiki>'''
# Print the sorted result using '''‘while loop’''' and '''special variable $_.'''
# Save and execute the program.
# Now check the result.
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Slide 18:
About Spoken Tutorial project
| style="border:1pt solid #000000;padding:0.097cm;"| The video at the following link summarises the Spoken Tutorial project.

Please download and watch it
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Slide 19:
About workshops
| style="border:1pt solid #000000;padding:0.097cm;"| The Spoken Tutorial Project Team
conducts workshops and gives certificates on passing online tests.

For more details, please write to us.
|-
| style="border:1pt solid #000000;padding:0.097cm;"| Slide 20:
Acknowledgement
| style="border:1pt solid #000000;padding:0.097cm;"| Spoken Tutorial project is funded by NMEICT, MHRD, Government of India.

More information on this mission is available at
this link.
|-
| style="border:1pt solid #000000;padding:0.097cm;"|
| style="border:1pt solid #000000;padding:0.097cm;"| This is Nirmala Venkat from IIT Bombay, signing off. Thanks for watching.
|}

@@ Line 32: / Line 32: @@
 | style="border:1pt solid #000000;padding:0.097cm;"| Slide 5:
 | style="border:1pt solid #000000;padding:0.097cm;"| What are''' special variables'''?
-'''Special variables''' are predefined variables that have a special meaning in '''Perl'''.
+*'''Special variables''' are '''predefined''' variables that have a special meaning in '''Perl'''.
-These do not need to be initialised before use.
+*These do not need to be initialised before use.
-These are used to hold the results of searches, '''environment variables''' and '''flags''' to control '''debugging'''.
+*These are used to hold the results of searches, '''environment variables''' and '''flags''' to control '''debugging'''.
 |-
 | style="border:1pt solid #000000;padding:0.097cm;"|
@@ Line 52: / Line 52: @@
 | style="border:1pt solid #000000;padding:0.097cm;"| Switch to the Terminal and type
 '''gedit special.pl''' &
-| style="border:1pt solid #000000;padding:0.097cm;"| I will open the''' special dot pl file''' which i have already created.
+| style="border:1pt solid #000000;padding:0.097cm;"| I will open the''' special dot pl file''' which I have already created.
-Go to the terminal and type''' gedit special.pl ampersand '''and press '''Enter.'''
+Go to the '''terminal''' and type''' gedit special.pl ampersand '''and press '''Enter.'''
 |-
 | style="border:1pt solid #000000;padding:0.097cm;"| Point the cursor''' special.pl'''
-| style="border:1pt solid #000000;padding:0.097cm;"| '''special.pl''' file is now open in '''gedit Text Editor'''.
+| style="border:1pt solid #000000;padding:0.097cm;"| '''special.pl''' file is now open in '''gedit'''.
 Type the code as displayed on the screen.
@@ Line 80: / Line 80: @@
 Both these''' foreach''' loops will execute the same result.
 In each iteration of the loop, the current string is placed in '''$_'''.
 And it is used by the '''print statement, '''by default.
 '''$_ '''saves the use of one extra variable '''$color'''.
@@ Line 96: / Line 98: @@
 |-
 | style="border:1pt solid #000000;padding:0.097cm;"| Highlight the output
-| style="border:1pt solid #000000;padding:0.097cm;"| Here both '''foreach''' loops gives the same output.
+| style="border:1pt solid #000000;padding:0.097cm;"| Here both '''foreach''' loops give the same output.
 |-
 | style="border:1pt solid #000000;padding:0.097cm;"|
@@ Line 131: / Line 133: @@
 '''Arguments''' for a '''subroutine''' are stored in this array variable.
-'''Array operations''' like '''pop/shift '''can be done on this '''variable''' as we do in normal '''arrays'''.
+'''Array operations''' like '''pop/shift '''can be done on this '''variable,''' as we do in normal '''arrays'''.
 |-
 | style="border:1pt solid #000000;padding:0.097cm;"| Switch to the Terminal and type
@@ Line 160: / Line 162: @@
 That is, it is stored under
-* dollar underscore index of zero
+* '''dollar underscore index of zero'''
-* and dollar underscore index of one
+* and '''dollar underscore index of one'''
 * i.e '''<nowiki>$_[0] </nowiki>'''and '''<nowiki>$_[1]</nowiki>'''
@@ Line 182: / Line 184: @@
 | style="border:1pt solid #000000;padding:0.097cm;"| Slide:8
 | style="border:1pt solid #000000;padding:0.097cm;"| '''Environment variables '''are represented by '''percentage '''followed by '''capital ENV'''.
 '''Environment variables '''contain a copy of the current '''environment variables, '''such as the following.
-* '''PWD, USER, LANG, PATH,''' etc.
 |-
 | style="border:1pt solid #000000;padding:0.097cm;"|
@@ Line 203: / Line 206: @@
 | style="border:1pt solid #000000;padding:0.097cm;"| Press''' Ctrl+S''' to save the file.
 Switch to the''' terminal''' and execute the '''Perl '''script.
 Type''' perl special dot pl''' and press''' Enter'''.
 |-
@@ Line 286: / Line 291: @@
 If the file '''hello.txt '''doesn't exist, it will print the error message,like:
-'''Cannot open file for reading : No such file or directory at main.pl line 3.'''
+'''Cannot open file for reading : No such file or directory.'''
 |-
 | style="border:1pt solid #000000;padding:0.097cm;"| Slide: 12
@@ Line 343: / Line 348: @@
 |-
 | style="border:1pt solid #000000;padding:0.097cm;"| Switch to '''sample.txt''' in gedit itself.
-| style="border:1pt solid #000000;padding:0.097cm;"| Let me show you the text that I have in a file named '''sample.txt'''
+| style="border:1pt solid #000000;padding:0.097cm;"| Let me show you the text that I have in a file named '''sample.txt''' file.
 |-
 | style="border:1pt solid #000000;padding:0.097cm;"| On the terminal type
@@ Line 352: / Line 357: @@
 | style="border:1pt solid #000000;padding:0.097cm;"| This is the text we had in '''sample.txt''' file.
-Note: If no files are specified, it reads from the '''STDIN''' (standard input). That is from the keyboard.
+If no files are specified, it reads from the standard input i.e. from the keyboard.
 <nowiki><<</nowiki>PAUSE>>
 |-
@@ Line 366: / Line 371: @@
 | style="border:1pt solid #000000;padding:0.097cm;"| '''Perl''' has an '''array''' '''at the rate capital A R G V '''special variable.
 This holds all the values from the '''command line'''.
 When using '''array''' '''at the rate capital A R G V, '''there is no need to declare the '''variables.'''
 The values from the '''command line''' are automatically placed in this '''variable'''.

@@ Line 12: / Line 12: @@
 Learning objectives
 | style="border:1pt solid #000000;padding:0.097cm;"| In this tutorial we will learn about
-* Global special variables
+* '''Global special variables'''
-* Special command line variables
+* '''Special command line variables'''
-* Global special constants
+* '''Global special constants'''
 |-
 | style="border:1pt solid #000000;padding:0.097cm;"| Slide 3:

@@ Line 470: / Line 470: @@
 | style="border:1pt solid #000000;padding:0.097cm;"| The Spoken Tutorial Project Team
 conducts workshops and gives certificates on passing online tests.
+|-
 | style="border:1pt solid #000000;padding:0.097cm;"|For more details, please write to us.
 |-

@@ Line 455: / Line 455: @@
 # '''my @numbers = ( 22, 88, 33, 55, 11);'''
 # Note: For descending order, use the below code for comparison.
-'''sort {$b<nowiki><=>$</nowiki>a} @numbers<nowiki>;</nowiki>'''
+#:'''sort {$b<nowiki><=>$</nowiki>a} @numbers<nowiki>;</nowiki>'''
 # Print the sorted result using '''‘while loop’''' and '''special variable $_.'''
 # Save and execute the program.
@@ Line 471: / Line 471: @@
 conducts workshops and gives certificates on passing online tests.
-For more details, please write to us.
+| style="border:1pt solid #000000;padding:0.097cm;"|For more details, please write to us.
 |-
 | style="border:1pt solid #000000;padding:0.097cm;"| Slide 20: