$a=key
$b=value
[download]

  DB<142> sub hgrep (&%) { 
           my $f=shift; 
           my @res;
           local ($a,$b); 
           while ( ($a,$b)= splice(@_,0,2) ) { 
             push @res, $a => $b  if $f->() 
           }
           return @res 
          }

  DB<143> %h = ( cat=>0, cut=>1, caty=>2 )
 => ("cat", 0, "cut", 1, "caty", 2)

  DB<144> hgrep { $a =~ /^cat/ } %h
 => ("cat", 0, "caty", 2)

  DB<145> hgrep { $b>1 } %h
 => ("caty", 2)
[download]

UPDATE: see Hash::MostUtils for a similar approach.