🐪

my $name = "John";
my $age = 25;
my $pi = 3.14;
my $undef;  # undefined

my @nums = (1, 2, 3, 4, 5);
my @mixed = ("a", 1, 2.5);
my $first = $nums[0];
my $len = scalar @nums;  # or $#nums + 1
push @nums, 6;
pop @nums;
shift @nums;
unshift @nums, 0;

my %person = (
  name => "John",
  age => 25,
);
my $name = $person{name};
$person{city} = "NYC";
delete $person{age};
my @keys = keys %person;
my @vals = values %person;

my $scalar_ref = \$name;
my $array_ref = \@nums;
my $hash_ref = \%person;

# Dereference
print $$scalar_ref;
print @$array_ref;
print %$hash_ref;

# Arrow notation
print $array_ref->[0];
print $hash_ref->{name};

my $str = "Hello";
my $len = length($str);
my $upper = uc($str);
my $lower = lc($str);
my $sub = substr($str, 0, 3);  # "Hel"
my $idx = index($str, "l");    # 2
my $concat = $str . " World";

my $name = "John";
print "Hello, $name!\n";       # Interpolates
print 'Hello, $name!\n';       # Literal
print "Array: @nums\n";        # Interpolates array
print "Hash key: $person{name}\n";

my $text = <<END;
This is a
multi-line
string.
END

if ($x > 10) {
  print "big";
} elsif ($x > 5) {
  print "medium";
} else {
  print "small";
}

unless ($logged_in) {
  print "Please login";
}

# Same as: if (!$logged_in)

my $status = $age >= 18 ? "adult" : "minor";

print "Hi" if $greet;
print "Error" unless $valid;
print $_ for @items;

for my $i (0..9) {
  print "$i\n";
}

foreach my $item (@items) {
  print "$item\n";
}

# C-style
for (my $i = 0; $i < 10; $i++) {
  print "$i\n";
}

while ($x < 10) {
  $x++;
}

until ($x >= 10) {
  $x++;
}

# do-while
do {
  $x++;
} while ($x < 10);

for my $i (1..10) {
  next if $i % 2 == 0;  # skip even
  last if $i > 7;        # break
  redo if $retry;        # restart iteration
  print "$i\n";
}

if ($str =~ /pattern/) {
  print "Match!";
}

if ($str !~ /pattern/) {
  print "No match";
}

# Case insensitive
if ($str =~ /pattern/i) { }

if ($str =~ /(\w+)@(\w+)/) {
  my $user = $1;
  my $domain = $2;
}

# Named captures
if ($str =~ /(?<user>\w+)@(?<domain>\w+)/) {
  print $+{user};
}

$str =~ s/old/new/;      # First occurrence
$str =~ s/old/new/g;     # Global
$str =~ s/old/new/gi;    # Global, case insensitive

# Transliteration
$str =~ tr/a-z/A-Z/;     # Uppercase

my @words = split /\s+/, $str;
my @parts = split /,/, $csv;
my $str = join ", ", @words;

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

my $msg = greet("World");

sub add {
  my ($a, $b) = @_;
  return $a + $b;
}

# Default values
sub greet {
  my ($name, $greeting) = @_;
  $greeting //= "Hello";
  return "$greeting, $name!";
}

sub min_max {
  my @nums = @_;
  my $min = (sort { $a <=> $b } @nums)[0];
  my $max = (sort { $b <=> $a } @nums)[0];
  return ($min, $max);
}

my ($min, $max) = min_max(3, 1, 4, 1, 5);

my $add = sub {
  my ($a, $b) = @_;
  return $a + $b;
};

print $add->(2, 3);

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

# Read entire file
my @lines = <$fh>;
my $content = do { local $/; <$fh> };

open(my $fh, ">", "file.txt") or die "Cannot open: $!";
print $fh "Hello, World!\n";
close($fh);

# Append
open(my $fh, ">>", "file.txt") or die $!;

-e $file  # exists
-f $file  # regular file
-d $file  # directory
-r $file  # readable
-w $file  # writable
-s $file  # size (bytes)
-z $file  # zero size

use strict;
use warnings;
use Data::Dumper;
use File::Path qw(make_path remove_tree);
use JSON qw(encode_json decode_json);

# MyModule.pm
package MyModule;
use strict;
use warnings;
use Exporter qw(import);
our @EXPORT_OK = qw(hello);

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

1;  # Module must return true