reverse hash, hash functions: keys values exists each

%ip_address = reverse %host_name;

it will reverse the value to key, the key to value of very item.

the value should be unique.

The keys function yields a list of all the keys in a hash, while the values function gives
the corresponding values. If there are no elements to the hash, then either function
returns an empty list:

my %hash = ("a" => 1, "b" => 2, "c" => 3);
my @k = keys %hash;
my @v = values %hash;

@k: a b c
@v: 1 2 3

 each function, which returns a key-value pair as a two-element
list

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

my %h = ("test"=>1,
        "this"=>2);

while (my ($key, $value) = each %h){
    print $key, $value;
}

To see whether a key exists in, use the exists function,

if(exists $hash{$key1}){
    print "can find it.";
}

The delete function removes the given key (and its corresponding value) from the hash.
my $person = "betty";
delete $books{$person};