perl: arrays and hashes

This is mostly a reminder for me than an article for everybody as I haven't touched perl for ages.

Small reference on arrays and hashes in perl.

Arrays

Declaration

@array = (1, '1', (2));
@array = (1..20);# by range

Access to array members with index

$array[0];

Define reference to array

$array = \@array; #reference to another array
$array = [1, 3, 5, 7, 9]; #reference to anonymous array
$array = [ @array ]; #reference to anonymous copy
@$array = (2, 4, 6, 8, 10); #implicit reference to anonymous array

To deference reference to array put @ or $ before $

@array = @$array;
@array = $$array;

Access to members of array by reference with index

$array->[0];# using -> operator
@$array[0];# dereferencing
$$array[0];# dereferencing

Size of the array

$#array;# [note: size of an empty array is -1, so $#array is a number of elements - 1]

Here is a tricks to remove all elements from an array, add an element to array

$#array = -1;
$c[++$#c] = 'value';

Take a slice of an array

@array[0..2];# first, second and third elements
@array[0,2];# first and third elements

Hashes

Declaration

%hash = ('key0', 'value0', 'key1', 'value1');# amount of elements must be even
%hash = ('key0' => 'value0', 'key1' => 'value1');

Access to hash members with key

$hash{'key0'};

Define reference to hash

$hash = \%hash; #reference to another hash
$hash = {1 => 3, 5 => 7}; #reference to anonymous hash
$hash = {1, 3, 5, 7}; #reference to anonymous hash; amount of elements must be even
$hash = [ %hash ]; #reference to anonymous copy
%$hash = (2, 4, 6, 8); #implicit reference to anonymous hash; amount of elements must be even
%$hash = (2 => 4, 6 => 8); #implicit reference to anonymous hash

To deference reference to hash put % or $ before $

%hash = %$hash;
%hash = $$hash;

Access to members of hash by reference with key

$hash->{'key0'};# using -> operator
%$hash[0];# dereferencing
$$hash[0];# dereferencing

Size of the hash

scalar keys(%hash)

Take a slice of a hash

@hash{'key0','key1'};
@hash{@keys};