※ 引述《sixth (12345(6))》之铭言：
: 请问如何让范例2 像 范例1 一样，印出计算结果?
: 范例1:
: eval '$sum = ((0x1 << 8) -1)';
: print "The sum is $sum\n";
: ==> 会印出 255
: 范例2:
: $str_test = "((0x1 << 8) -1)";
: eval '$sum = $str_test';
: print "The sum is $sum\n";
: ==> 会印出 (0x1 << 8) -1)
自问自答，改成这样就可以了
$str_test = "((0x1 << 8) -1)";
$do_eval = "\$sum = $str_test";
eval $do_eval;
print "The sum is $sum\n";