This is such a frequently reinvented wheel! 8)

IMHO something like hgrep() or hmap() should be somewhere in the core-moduls... with a code-prototype it's easy to accomplish.

Anyway TIMTOWTDI:

Without explicit grep

%hash_2= map { /regex/ ? ( $_ , $hash_1{$_} ) 
                       : () 
           } keys %hash_1;
[download]

Hashslice:

my @keys = grep { /regex/ } keys %hash_1;
@hash_2{@keys} = @hash_1{@keys};
[download]

http://www.perl-community.de/bat/poard/message/120873