Perl Tutorial

• Introduction to Perl
• Installation and Environment Setup
• Syntax of a Perl Program
• Hello World Program in Perl
• Perl vs C/C++
• Perl vs Java
• Perl vs Python

Fundamentals

• Modes of Writing a Perl Code
• Boolean Values
• Operators
• Variables
• Variables and its Types
• Scope of Variables
• Modules in Perl
• Packages in Perl
• Number and its Types
• Directories with CRUD operations

Input and Output

• Use of print() and say() in Perl
• Perl | print operator
• Use of STDIN for Input

Control Flow

• Decision Making
• Loops
• Perl given-when Statement
• Perl goto operator
• next operator
• redo operator
• last in loop

Arrays and Lists

• Arrays
• Array Slices
• Getting the Number of Elements of an Array
• Reverse an array
• Sorting of Arrays
• Useful Array functions
• Arrays (push, pop, shift, unshift)
• Implementing a Stack
• List and its Types
• List Functions

Hash

• Introduction to Hash
• Working of a Hash
• Hash Operations
• Sorting a Hash
• Multidimensional Hashes
• Hash in Scalar and List Context
• Useful Hash functions

Scalars

• Scalars
• Comparing Scalars
• scalar keyword

Strings

• Quoted, Interpolated and Escaped Strings
• Multi-line Strings | Here Document
• Sorting mixed Strings in Perl
• String Operators
• Useful String Operators
• String functions (length, lc, uc, index, rindex)
• Useful String functions
• Automatic String to Number Conversion or Casting
• Count the frequency of words in text
• Removing leading and trailing white spaces (trim)

Object Oriented Programming in Perl

• Introduction to OOPs
• Classes
• Objects
• Methods
• Constructors and Destructors
• Method Overriding
• Inheritance
• Polymorphism
• Encapsulation

Subroutines

• Subroutines or Functions
• Function Signature in Perl
• Passing Complex Parameters to a Subroutine
• Mutable and Immutable parameters
• Multiple Subroutines
• Use of return() Function
• References
• Pass By Reference
• Recursion in Perl

Regular Expressions

• Regular Expressions
• Operators in Regular Expression
• Regex Character Classes
• Special Character Classes in Regular Expressions
• Quantifiers in Regular Expression
• Backtracking in Regular Expression
• ‘e’ modifier in Regex
• ‘ee’ Modifier in Regex
• pos() function in Regex
• Regex Cheat Sheet
• Searching in a File using regex

File Handling

• File Handling Introduction
• Opening and Reading a File
• Writing to a File
• Appending to a File
• Reading a CSV File
• File Test Operators
• File Locking
• Use of Slurp Module
• Useful File-handling functions

Context Sensitivity

• Scalar Context Sensitivity
• List Context Sensitivity
• STDIN in Scalar and List Context

CGI Programming

• CGI Programming
• File Upload in CGI
• GET vs POST in CGI

Misc

• Breakpoints of a Debugger
• Exiting from a Script
• Creating Excel Files
• Reading Excel Files
• Number Guessing Game using Perl
• Database management using DBI
• Accessing a Directory using File Globbing
• Use of Hash bang or Shebang line
• Useful Math functions

Reverse an array in Perl

Reversing an array is a fundamental operation in programming, and Perl provides a straightforward way to achieve this. Here's a tutorial on how to reverse an array in Perl:

1. Introduction

In Perl, the reverse function can be used not only for reversing strings but also for reversing arrays.

2. Basic Usage

Using the reverse function:

To reverse an array, you can use the reverse function.

my @original = (1, 2, 3, 4, 5);
my @reversed = reverse @original;

print "@reversed\n";  # Outputs: 5 4 3 2 1

3. Reversing In-Place

If you want to reverse an array in-place, meaning you want to modify the original array without creating a new one, you can do the following:

my @array = (1, 2, 3, 4, 5);
@array = reverse @array;

print "@array\n";  # Outputs: 5 4 3 2 1

4. Reversing a Range

Perl allows you to create a range of numbers using the .. operator. This range can be reversed using the reverse function:

my @range = (1..10);
my @reversed_range = reverse @range;

print "@reversed_range\n";  # Outputs: 10 9 8 7 6 5 4 3 2 1

5. Using reverse in Scalar Context

It's essential to understand that the behavior of reverse changes when used in a scalar context. In scalar context, reverse treats its argument as a string:

my $string = "hello";
my $reversed_string = reverse $string;

print "$reversed_string\n";  # Outputs: olleh

6. Reversing Multi-dimensional Arrays

If you're working with multi-dimensional arrays (like an array of arrays), remember that the reverse function will only reverse the top-level elements:

my @multi = ( [1, 2, 3], [4, 5, 6], [7, 8, 9] );
my @reversed_multi = reverse @multi;

# Print the reversed multi-dimensional array
foreach my $ref (@reversed_multi) {
    print "@$ref\n";  # Outputs: 7 8 9, then 4 5 6, and finally 1 2 3
}

If you want to reverse the inner arrays as well, you'll have to loop through each of them and apply the reverse function.

7. Summary

Reversing arrays in Perl is straightforward using the reverse function. This function provides a quick way to reverse the order of the elements in an array, and by understanding its behavior in different contexts, you can manipulate arrays and strings effectively.

1. Reversing an array in Perl example:

   • Description: The reverse() function in Perl can be used to reverse the order of elements in an array.
   • Code Example:

     my @numbers = (1, 2, 3, 4, 5);
     my @reversed_numbers = reverse @numbers;
     
     print "Original array: @numbers\n";
     print "Reversed array: @reversed_numbers\n";
     

2. Using the reverse function in Perl:

   • Description: The reverse() function reverses the order of elements in a list or array.
   • Code Example:

     my @colors = qw(red green blue);
     my @reversed_colors = reverse @colors;
     
     print "Original colors: @colors\n";
     print "Reversed colors: @reversed_colors\n";
     

3. In-place array reversal in Perl:

   • Description: In-place array reversal can be done using array slicing and the reverse() function.
   • Code Example:

     my @fruits = qw(apple banana cherry);
     @fruits = reverse @fruits;
     
     print "Reversed fruits: @fruits\n";
     

4. Perl reverse array elements:

   • Description: Array elements can be reversed using indices and swapping.
   • Code Example:

     my @letters = ('A', 'B', 'C', 'D');
     my $length = scalar @letters;
     
     for my $i (0..($length/2 - 1)) {
         my $temp = $letters[$i];
         $letters[$i] = $letters[$length-$i-1];
         $letters[$length-$i-1] = $temp;
     }
     
     print "Reversed letters: @letters\n";
     

5. Reversing an associative array in Perl:

   • Description: Reversing an associative array involves reversing the order of keys or values.
   • Code Example (Reversing order of keys):

     my %ages = ('Alice' => 30, 'Bob' => 25, 'Charlie' => 35);
     my @reversed_keys = reverse keys %ages;
     
     print "Original keys: ", join(', ', keys %ages), "\n";
     print "Reversed keys: ", join(', ', @reversed_keys), "\n";
     

6. Using array slices for reversal in Perl:

   • Description: Array slices can be used to reverse a portion of an array.
   • Code Example:

     my @numbers = (1, 2, 3, 4, 5);
     @numbers[1, 2, 3] = reverse @numbers[1, 2, 3];
     
     print "Reversed subset: @numbers\n";
     

7. Perl reverse vs reverse in scalar context:

   • Description: In scalar context, reverse concatenates the elements rather than reversing the order.
   • Code Example:

     my @letters = ('A', 'B', 'C');
     my $reversed_string = reverse @letters;
     
     print "Reversed string: $reversed_string\n";
     

8. Array reversal without using the reverse function in Perl:

   • Description: Array reversal without using reverse involves using indices and swapping.
   • Code Example:

     my @animals = ('cat', 'dog', 'elephant', 'monkey');
     my $length = scalar @animals;
     
     for my $i (0..($length/2 - 1)) {
         my $temp = $animals[$i];
         $animals[$i] = $animals[$length-$i-1];
         $animals[$length-$i-1] = $temp;
     }
     
     print "Reversed animals: @animals\n";