This document provides an overview of the Perl programming language. It discusses that Perl uses an interpreter to run code without compilation, and that it is easy to learn, program, and debug in Perl. The document then covers Perl installation, variables, data types, control structures, modules, and provides an example of a basic phonebook program to demonstrate hashes.

1. Practical Approach to PERL
Rakesh Mukundan

2. Scripting Language

Uses an interpreter to run the code

No compilation needed, just run it!

Interpreted line by line

Fast to learn and program

Easy debugging

Every user is a developer :)

3. PERL
• Practical Extraction and Report Language
• Also known as Practically Everything
Really Likeable
• Began as the result of one man's frustration
and, by his own account, inordinate laziness 
• Perl is free. The full source code and
documentation are free to copy, compile,
print, and give away

4. Why Learn Perl
• Perl is easy and it makes life easy!
• Its open source
• Lots of tested modules available for re-use
• You are too lazy to do mechanical repetitive
work 

5. Do You Have Perl Installed?
• Execute the following command in a shell
– perl -v

6. Installation
• UNIX and Linux : Available with installation CD or
standard repositories if not installed by default
• Windows : Many flavors are available with and without
IDEs, free and proprietary etc
– Active State Perl
– Strawberry Perl

7. Your First Perl Program
• Open MyFirstProgram.pl from the examples directory
with your favorite text editor ( gedit,vim,notepad++
etc )
• To run the program open up a shell and navigate to
the examples directory
• perl MyFirstProgram.pl
• In Linux systems perl file can be directly executed,
provided path to interpreter has been specified
correctly.
• chmod a+x MyFirstProgram.pl
• ./MyFirstProgram.pl

8. Under the hood
Location of interpreter
Comment
A perl statement
terminated with a
semi-colon

9. Variables
• Place to store data
• A scalar variable stores a single value
• Perl scalar names are prefixed with a dollar
sign ($)
– Ex: $name,$password,$ip_address
• No need to define a variable explicitly, use
directly
• A scalar can hold data of any type, be it a
string, a number, or whatnot

10. Examples of Variables
• $floating_val = 3.14
• $integer_val = 1008
• $string_val = “My String”
• $hashReff = %HashToPoint;
• $SubReff = MyRoutine();
• $ScalarReff = $floating_val;

11. Numerical Operations
Addition : $var1 + $var2
Subtraction : $var1 - $var2
Multiplication: $var1 * $var2
Division: $var1 / $var2
Increment: $var++
Power: $var1 ** $var2
Modulus: $var1 % $var2;

12. Contd..

Greater than: $var1 > $var2

Greater than or equal: $var1 >= $var2

Less than : $var1 < $var2

Less than or equal: $var1<= $var2

Equality: $var1== $var2

13. Strings
An string of characters, no size limit
 “Hello World”
Can be specified using single quotes(') or
double quotes(“)
Strings can be concatenated using dot (.)
operator
No operations are possible inside a single
quoted string
 “1 plus 2 is $value”
 '1 plus 2 is $value'

14. Strings
An string of characters, no size limit
 “Hello World”
Can be specified using single quotes(') or
double quotes(“)
Strings can be concatenated using dot (.)
operator
No operations are possible inside a single
quoted string
 “1 plus 2 is $value”
 '1 plus 2 is $value'

15. Special Characters
L Transform all letters to lowercase
l Transform the next letter to lowercase
U Transform all letters to uppercase
u Transform the next letter to uppercase
n Begin on a new line
r Apply a carriage return
t Apply a tab to the string
EEnds U, L functions

16. Print Function
Most commonly used perl function
Can print a variable or string to
console/file/any file handle
Usage print <file handle> expression
By default prints to STDOUT
 Print “Hello World n”;
 Print $MyVariable;
 Print “My name is $MyVariable n”;
 Print “One plus one is always 1+1 n”;

17. User Input

<STDIN> stands for standard input

Program waits for user to enter an input

It will contain newline character also

$MyAge= <STDIN>;

chomp($MyAge);

18. Calculator Program
Ask user to enter two numbers
Do all the numerical operations mentioned in
previous slide and print the output

19. String Operations
index(STR,SUBSTR) :Returns the position of
the first occurrence of SUBSTR in STR
length(EXPR) :Returns the length in
characters of the value of EXPR
rindex(STR,SUBSTR) :Works just like index
except that it returns the position of the
LAST occurrence of SUBSTR in STR
substr(EXPR,OFFSET,LEN):Extracts a sub
string out of EXPR and returns it

20. Array
• List of scalars
• Similar to arrays in C,C++ etc..
• Array is identified by @ symbol
• @FirstArray = (“one”,”two”,”three”);
• Each element can be accessed by its
corresponding index
• print $FirstArray[2];

21. Arrays

22. Visualizing Data In Perl

Use the Dumper module
 use Data::Dumper;

print Dumper $ref;

$ref is the refference to the variable

print Dumper @Array;

print Dumper %Hash;

23. Working With Arrays
• An array element can be indexed as
$MyFirstArray[1]
• push() - adds an element to the end of an
array.
• unshift() - adds an element to the beginning
of an array.
• pop() - removes the last element of an array.
• shift() - removes the first element of an
array.

24. A phonebook
• Pallava => 3001
• Krishna => 3002
• Godhavari => 3003
• Kaveri => 3004
• How do you represent such a list?
– Lookup by names?

25. Hashes
• Hash is a like a phone book which has names
and corresponding phone numbers
• Each element in a hash will have a key and
value
• For example
– %PhoneBook = (
• “pallava” => 3001,
• “krishna” => 3002,
• “godhavari”=> 3003,
• “kaveri” => 3004);

26. Hashes

27. Working With Hash Values
• Each value can be accessed by its key
– $Phonebook{“pallava”}
• To add a new value to hash table
– $Phonebook{“nilgiris”} =”3005”;
• To delete a value from hash table
– delete($Phonebook{“nilgiris”});
• Looping through a hashtable
– while (($key, $value) = each(%Phonebook)){
– Print $key.$value;
–}

28. Contd..
• Checking if a particular key has already added in the
hash table
– if (exists($Phonebook{"pallava"}))
–{
–}

29. Program Control
• If
• While
• For
• Foreach

30. if
•
Conditional statement to check if a criteria is
met or not
•
The syntax is
•
if(condtion){ code to execute;}
•
if($var1 ==5){
•
print “variable is 5n”;
•
}

31. ifelse

Else is the compliment of if

Execute code if the condition is not met

Syntax

if(condition){ code for condition met}

else{ code for condition false}

if($var1==5){

print “variable value is 5n”;

}

else{

Print “variable value is not 5n”;

}

32. elsif
if(condition1){
Code to execute
}
elsif(condition2){
Code to execute
}
Else{
Code to execute
}

33. while
•
Loop while the condition is true
•
while($count<5){
•
Print “Cont:$countn”;
•
$count++;
•
}
•
While(1) makes an infinite loop
•
Flow Control
•
next :go to the next iteration
•
last:end while loop

34. for
•
A for loop counts through a range of
numbers, running a block of code
each time it iterates through the loop
•
for(initial, condition, $increment)
{ code to execute }
•
for($count=0;$count<11;$count++)
{
•
Print “Count $count n”;
•
}

35. foreach
•
Used for iterating over an array or hash
•
foreach(@MyArray){
•
print “Element : $_n”;
•
}

36. Phonebook Program

Print existing numbers

Option to add a new entry

Option to delete and entry

Option to exit the program

Option to search by name

37. Strict Usage
By default perl doesn't need any variable to be
declared before use
Simple spelling mistakes in variable names can
lead to hours of code debugging!
By using the strict method,perl will strictly ask
you declare variable
 my $MyFirstVar;
 my @MyFirstArray;
 my %MyFirstHash;