#!/usr/bin/perl

# http://perlmonks.org/?node_id=1185598

use strict;
use warnings;

my @array = qw(world today is very nice);
my %hash = (0 => "Hello", 1=> "world" , 2=> "today" , 3=> "is" , 4=> "nice",
  5=> "is");

my %reversehash; # allow for different keys mapping to the same value
push @{ $reversehash{$hash{$_}} }, $_ for keys %hash;

my @newarray = map @{ $reversehash{$_} // [] }, @array;

use Data::Dumper; print Dumper \@newarray;