印出陣列@hash_array中每個雜湊鍵為'birthday'的值，如果雜湊鍵不存在，就印出「不存在」來提醒使用者。

#ref_exercise2.pl




%hash1 = ( name => 'Paul',
            age => 21,
     cellphone => '0922222222',
     birthday => '1982/3/21' );
   
%hash = ( name => 'John',
          age => 24,
    cellphone => '0911111111' );


@array_hash = (\%hash1,\%hash);


for $hash_ref (@array_hash){
    print ${$hash_ref}{birthday}."\n";
    if (!${$hash_ref}{birthday}){print "DOES NOT EXIST!\n"}
}