问题
I've entered a command cd // instead of cd / by mistake and instead of getting an error as I'd expect the shell (Bash) showed a prompt as if I'm in the // directory:-
<username>@<hostname>://$
<username>@<hostname>://$ pwd
//
Listing the content of the directory shows that it is the same as /.
So what exactly cd // do and what's the difference from cd /?
回答1:
Actually it means nothing and is ignored.
From the Bash FAQ E10::
E10) Why does 'cd //' leave $PWD as '//'?
POSIX.2, in its description of 'cd', says that three or more leading slashes may be replaced with a single slash when canonicalizing the current working directory.
This is, I presume, for historical compatibility. Certain versions of Unix, and early network file systems, used paths of the form //hostname/path to access 'path' on server 'hostname'.
Also the Unix standards states:
A pathname that begins with two successive slashes may be interpreted in an implementation-defined manner, although more than two leading slashes shall be treated as a single slash.
回答2:
This answer on AskUbuntu confirms that they are the same directory. Further, it helpfully quotes from the POSIX Pathname Resolution specification:
A pathname consisting of a single slash shall resolve to the root directory of the process. A null pathname shall not be successfully resolved. A pathname that begins with two successive slashes may be interpreted in an implementation-defined manner, although more than two leading slashes shall be treated as a single slash.
来源：https://stackoverflow.com/questions/20690828/what-does-double-slash-in-cd-mean-in-linux