#!/usr/bin/perl        # "hash-bang" line

# this is a comment line

# some declarations with the use clause
# =====================================

use warnings;   # it warns about undefined values
use strict;     # it's a lexically scoped declaration

# a simple statement
# ==================
 
# the next code initializes $pi scalar variable
# any scalar variable begins with $ symbol

my $pi = 3.14;    # the statement ends in a semicolon

# a conditional statement
# =======================

# also note the numeric operator == and 
# the use of the print function

print "pi = $pi\n" if $pi == 3.14;
# it will output pi = 3.14

# a while loop statement
# ======================

my @numbers = ();   

# this line declares and empties the 
# @numbers array variable;
# any array variable begins with the @ symbol

while(my $line = <STDIN>)
{
  chomp $line;
  push(@numbers, $line);
}

# we read some lines from <STDIN> using the
# $line scalar variable
# chomp function will remove the ending newline
# push function will append the read number 
# to @numbers array
# the loop will end when we type Ctrl/Z

# calling a subroutine
# ====================

# in the following lines we will declare and 
# call a subroutine that will add two numbers
# and it will return their sum

sub add2Numbers
{
  my $firstNumber = $_[0];    # first argument
  my $secondNumber = $_[1];   # second argument
  return $firstNumber + $secondNumber;
}

# calling the subroutine declared above:

print add2Numbers(3, 5), "\n";

# it will output 8

# using a module
# ==============

# the following snippet code will show you
# how to use a module in your script;
# we’ll exemplify with the DateTime-0.47 module;
# in order to run this script you must have 
# already installed this module on your system

use DateTime;

# the module must be declared first through use clause

my $dt = DateTime->now;

# $dt variable is initializes with the current date

print "Current Date:\n";
print "Month:", $dt->month, "\n";
print "Day:", $dt->day, "\n";
print "Year:", $dt->year, "\n";

# it will print the current month, day and year