my %hash2 = @hash{ grep /\d+_\d+/, keys %hash }; #### my %hash2; @hash2{ @$_ } = @hash{ @$_ } for [ grep /\d+_\d+/, keys %hash ]; # or more verbosely my %hash2; { my @key = grep /\d+_\d+/, keys %hash; @hash2{ @key } = @hash{ @key }; }