It doesn't work on the hash or array container, but does work with their scalar elements:

use warnings;
use strict;

my %hash = (one => 1, two => 2);

for my $key (keys %hash){
    print "$key\n" if $key =~ /one/;
}

my @array = qw(one two three);

for my $elem (@array){
    print "$elem\n" if $elem =~ /one/;
}
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