Perl Cheat Sheet

print "Hello, World!\n";

#!/usr/bin/perl
use strict;
use warnings;

# Single line comment

=begin
Multi-line comment
=cut

print "No newline";
say "With newline";  # Requires use 5.010

perl script.pl
perl -e 'print "code\n"'  # One-liner

my $name = "John";
my $age = 30;
my $price = 19.99;

my @fruits = ("apple", "banana", "cherry");
my @numbers = (1, 2, 3, 4, 5);

my %person = (
    name => "John",
    age => 30,
    city => "NYC"
);

$fruits[0];        # "apple"
$fruits[-1];       # Last element
scalar(@fruits);   # Length

$person{name};     # "John"
keys %person;      # ("name", "age", "city")
values %person;    # Values

my $arrayref = \@fruits;
my $hashref = \%person;
$arrayref->[0];    # Access
$hashref->{name};  # Access

my $value = undef;
if (!defined($value)) { print "undef\n"; }

$a + $b;  # Addition
$a - $b;  # Subtraction
$a * $b;  # Multiplication
$a / $b;  # Division
$a % $b;  # Modulus
$a ** $b; # Exponent

$str . $str2;  # Concatenation
$str x 3;      # Repeat 3 times
$str eq $str2; # String equal
$str ne $str2; # String not equal

$a == $b;  # Equal
$a != $b;  # Not equal
$a > $b;   # Greater
$a < $b;   # Less
$a >= $b;  # Greater or equal
$a <= $b;  # Less or equal

$a eq $b;  # Equal
$a ne $b;  # Not equal
$a gt $b;  # Greater
$a lt $b;  # Less
$a ge $b;  # Greater or equal
$a le $b;  # Less or equal

$a && $b;  # AND
$a || $b;  # OR
!$a;       # NOT
$a and $b; # Low precedence AND
$a or $b;  # Low precedence OR

1..10;        # (1,2,3,4,5,6,7,8,9,10)
'a'..'e';     # ('a','b','c','d','e')

if ($age > 18) {
    print "Adult";
} elsif ($age > 12) {
    print "Teen";
} else {
    print "Child";
}

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

my $status = $age >= 18 ? "Adult" : "Minor";

print "Yes" if $condition;
die "Error" unless $ok;

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

foreach my $fruit (@fruits) {
    print "$fruit\n";
}

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

until ($done) {
    # code
}

last;     # Break
next;     # Continue
redo;     # Restart iteration

print "$_\n" for @array;
print "$_\n" while <STDIN>;

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

my $msg = greet("John");
greet("John");  # Without parens

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

sub greet {
    my $name = shift // "Guest";
    return "Hello, $name!";
}

sub modify {
    my $arrayref = shift;
    push @$arrayref, "new";
}

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

$str =~ s/old/new/;    # First match
$str =~ s/old/new/g;   # Global (all)

if ($str =~ /(\d+)-(\d+)/) {
    print "First: $1, Second: $2";
}

/pattern/i;  # Case insensitive
/pattern/g;  # Global
/pattern/m;  # Multi-line
/pattern/s;  # Single-line (. matches \n)

my @parts = split(/,/, $str);
my @words = split(/\s+/, $text);

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

open(my $fh, '>', 'output.txt') or die $!;
print $fh "Hello\n";
close($fh);

open(my $fh, '>>', 'file.txt') or die $!;
print $fh "Appended\n";
close($fh);

open(my $fh, '<', 'file.txt') or die $!;
my $content = do { local $/; <$fh> };
close($fh);

if (-e 'file.txt') { print "Exists"; }
if (-f 'file.txt') { print "Is file"; }
if (-d 'dir') { print "Is directory"; }