为什么“.”在chown工作？

Question

为什么GNU chown user.group能工作？文档更不用说所支持的语法了。背后有什么有趣的故事吗？

Answer 1

info chown对此很清楚：

Some older scripts may still use `.' in place of the `:' separator.
POSIX 1003.1-2001 (*note Standards conformance::) does not require
support for that, but for backward compatibility GNU `chown' supports
`.' so long as no ambiguity results. New scripts should avoid the use
of `.' because it is not portable, and because it has undesirable
results if the entire OWNER`.'GROUP happens to identify a user whose
name contains `.'.

对于GNU程序，它不仅值得检查man，而且还值得检查info页面，因为GNU厌恶手册页(来自man tar)。