If you want to avoid to build a hash of arrays, you could concatenate the key strings with a delimiter that does not exist in the values. Something like 

my %rev;
while( my( $key, $val) = each %hash ) {
  $rev{$val} .= "|$key";
}

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In reply to Re: Find common values in a hash and print the respective keys by hdb
in thread Find common values in a hash and print the respective keys by Anonymous Monk

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