※ 引述《sixth (12345(6))》之銘言：
: 請問如何讓範例2 像 範例1 一樣，印出計算結果?
: 範例1:
: eval '$sum = ((0x1 << 8) -1)';
: print "The sum is $sum\n";
: ==> 會印出 255
: 範例2:
: $str_test = "((0x1 << 8) -1)";
: eval '$sum = $str_test';
: print "The sum is $sum\n";
: ==> 會印出 (0x1 << 8) -1)
自問自答，改成這樣就可以了
$str_test = "((0x1 << 8) -1)";
$do_eval = "\$sum = $str_test";
eval $do_eval;
print "The sum is $sum\n";