in reply to how can i return the common keys from a hash

Use another hash to count the keys: (Corrected: Pre- not post-increment) 

%h= 1..10; %i = 1.. 20; %j = 3..8; %k = 9 .. 18;; %l = 1 .. 14;;
%x = ();;
print grep{ 
    ++$x{ $_ } == 2 
} sort{ 
    $a <=> $b 
} map{ 
    keys %$_ 
} \( %h, %i, %j, %k, %l,);;
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