Make the last line of

sub query_databases {
....
 return \%dbs;
}
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Call it so:

my $dbsref = query_databases ();
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Then pass that to do_compare()

my $result = do_compare( $dbsref );
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Within do_compare() us the passed hashref

sub do_compare {
  my $dbsref = shift;
  for my $key ( keys %$dbsref ) {
    if ($dbsref->{$key}{ORACLE1} eq $dbsref->{$key}{ORACLE1}) {
        # the same
    } else {
        # different
    }
  }
 }
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