push @{ $no_name_found { $user_name } }, $city;
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The value associated with the key is an array reference, and so

        my $value = $result->{$key};
        print "User Name = $key - City: $value\n";
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will output something that looks like

User Name = User - City: ARRAY(0x3eafa1c)
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You might get something closer to what you expect with

        my $value = $result->{$key};
        local $" = ', ';
        print "User Name = $key - City: @$value\n";
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or

        my $value = $result->{$key};
        print "User Name = $key - City: ", join(', ', @$value), "\n";
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or something similar.