somebody cannot but do something?是正式短語，通常用于書面，不用于口語，意為“不得不”。

多種表達“不得不…；非…不可；不禁…”的短語如下，cannot可縮寫為can't：

can't help being so cute

書面：
cannot but do
cannot choose but do

- I cannot but admire her. 我不得不佩服她。
- I cannot choose but go at once. 我不得不馬上去。

口語：
cannot help but do
cannot help doing【注意cannot help后面的兩種不同動詞形式】
cannot help oneself from doing
have no (other) choice/alternative but to do【注意有to】

- I cannot help laughing. 我不禁笑起來。
- I had no choice but to resign. 我不得不辭職。