@a1_index{ @a1 } = 0..$#a1;

##</code><code>##

my @a1 = ( qw(one two three four five six seven eight nine ten) );
my @a2 = ( qw(four seven nine) );

##</code><code>##

@indices = ( qw( 3 6 8) );

##</code><code>##

use strict;
use warnings;

use Data::Dumper;

my @a1 = ( qw(one two three four five six seven eight nine ten) );
my @a2 = ( qw(four seven nine) );

my @indices;
my $c=0;
map { 
	foreach my $i (@a2) {
		if($_ eq $i) {push(@indices, $c)};
	}
	$c++;
} @a1;

print "indices DUMP:\n", Dumper(\@indices), "\n";