How can you get the keys of a Hash in Perl?

#!/usr/bin/perl

%FM = ( 'Radio City' => 91.1,
              'Big FM' => 92.7,
              'Red FM' => 93.5,
              'Radio One' => 94.3,
              'Radio Mirchi' => 98.3,
              'FM Gold' =>100.7,
              'Fever' => 104.0,
              'Oye FM' => 104.8,
              'FM Rainbow' => 107.1);

#get keys only
foreach my $key (sort keys %FM)
{
        print "$key\n";
}