How can I also get an element's index when I grep through an array?

Question

Let's say I have this list:

my @list = qw(one two three four five);

and I want to grab all the elements containing o. I'd have this:

my @containing_o = grep { /o/ } @list;

But what would I have to do to also receive an index, or to be able to access the index in grep's body?

Answer 1

 

my @index_containing_o = grep { $list[$_] =~ /o/ } 0..$#list;  # ==> (0,1,3)

my %hash_of_containing_o = map { $list[$_]=~/o/?($list[$_]=>$_):() } 0..$#list
            # ==> ( 'one' => 0, 'two' => 1, 'four' => 3 )