Learn perl with examples www.rakeshmukundan.in

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;