搞错了，应该是getopt(3). getopt(1)是util-linux里的一个程序，getopt(3)才是POSIX函数。关于"--"的描述getopt(3)是这么说的。

       By default, getopt() permutes the contents of argv as it scans, so that
       eventually all the nonoptions are at the end.  Two other scanning modes
       are  also  implemented.   If the first character of optstring is '+' or
       the environment variable POSIXLY_CORRECT is set, then option processing
       stops  as  soon  as  a nonoption argument is encountered.  If the first
       character of optstring is '-', then each nonoption argv-element is han‐
       dled  as  if  it  were the argument of an option with character code 1.
       (This is used by programs that were written to expect options and other
       argv-elements  in  any  order  and  that care about the ordering of the
       two.)  The special argument "--" forces an end of  option-scanning  re‐
       gardless of the scanning mode.

【 在 gnwd (gnwd) 的大作中提到: 】
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