Perl Cheatsheet

$age = 30;  # Scalar
$name = "John";  # String
@numbers = (1, 2, 3);  # Array
%person = ('name' => 'John', 'age' => 30);  # Hash

# Contexts
my @array = (1, 2, 3);
my $count = @array;  # Scalar context returns length

# Arrays and Hashes
my @fruits = ('apple', 'banana', 'orange');
my %person = ( 'name' => 'John', 'age' => 30 );

# If-else
if ($age > 18) {
  print "Adult";
} else {
  print "Minor";
}

# Loops
for my $i (1..5) {
  print "$i\n";
}

my $i = 0;
while ($i < 5) {
  print "$i\n";
  $i++;
}

# Unless (reverse if)
unless ($age > 18) {
  print "Minor";
}

sub greet {
  my ($name) = @_;
  return "Hello, $name";
}

print greet("John");  # Output: Hello, John

# Subroutine with multiple return values
sub calculate {
  my ($a, $b) = @_;
  return ($a + $b, $a * $b);
}

my ($sum, $product) = calculate(5, 10);
print "$sum, $product";  # Output: 15, 50

# Match operator
if ($text =~ /pattern/) {
  print "Match found";
}

# Substitute operator
$text =~ s/foo/bar/g;

# Capture groups
if ($text =~ /(\d+)/(\w+)/) {
  print "$1, $2";
}

open(my $fh, '<', 'file.txt') or die "Cannot open file: $!";
while (my $line = <$fh>) {
  print $line;
}
close($fh);

# Writing to a file
open(my $out, '>', 'output.txt') or die "Cannot open file: $!";
print $out "Hello, Perl!";
close($out);

# Scalar reference
my $x = 10;
my $ref_x = \$x;
print $$ref_x;  # Dereference scalar reference

# Array reference
my @arr = (1, 2, 3);
my $arr_ref = \@arr;
print @{$arr_ref};  # Dereference array reference

# Hash reference
my %hash = ('a' => 1, 'b' => 2);
my $hash_ref = \%hash;
print %{$hash_ref};

# Loading a module
use Math::Trig;

print tan(1);

# Custom package
package MyPackage;
sub hello {
  print "Hello from MyPackage!";
}

# Use in script
use MyPackage;
MyPackage::hello();

package Animal;
sub new {
  my $class = shift;
  my $self = { 'name' => shift };
  bless $self, $class;
  return $self;
}

sub speak {
  my $self = shift;
  print "$self->{name} makes a sound";
}

package Dog;
use parent 'Animal';

sub speak {
  my $self = shift;
  print "$self->{name} barks";
}

# Creating objects
my $dog = Dog->new("Rex");
$dog->speak();  # Output: Rex barks

# Using eval for error handling
eval {
  die "Something went wrong";
};

if ($@) {
  print "Error: $@";
}

# Raising exceptions
die "Fatal error!";

# Nested data structures
my $person = {
  'name' => 'John',
  'age' => 30,
  'address' => {
    'city' => 'New York',
    'zip' => '10001'
  }
};

print $person->{'name'};  # John
print $person->{'address'}->{'city'};  # New York

# Signal handling
$SIG{'INT'} = sub {
  print "Caught SIGINT!\n";
  exit;
};

while (1) {
  print "Running...\n";
  sleep(1);
}

my $arg1 = $ARGV[0];
my $arg2 = $ARGV[1];
print "Argument 1: $arg1, Argument 2: $arg2\n";

# Iterating over command line args
foreach my $arg (@ARGV) {
  print "Arg: $arg\n";
}

# Sorting hash keys
my %person = ('name' => 'John', 'age' => 30);
foreach my $key (sort keys %person) {
  print "$key: $person{$key}\n";
}

# Sorting arrays
my @numbers = (5, 2, 9, 1);
my @sorted = sort { $a <=> $b } @numbers;
print "Sorted: @sorted";

use threads;

sub task {
  my $id = shift;
  print "Thread $id running\n";
}

# Create threads
my $t1 = threads->create('task', 1);
my $t2 = threads->create('task', 2);

# Join threads
$t1->join();
$t2->join();

# Scalar context
my @arr = (1, 2, 3);
my $count = @arr;  # Returns number of elements
print "$count\n";  # Output: 3

# List context
my ($first, $second) = @arr;
print "$first, $second\n";  # Output: 1, 2