Re: cd"": Shouldn't it fail?

[Chet Ramey]

On 1/27/24 10:30 PM, jwo@jwo.cz wrote:
> Hello,
>
> (If you don't want to read through this stuff, see the end or grep for
>   word ``opinion''.)
>
> I started exploring details of file handling on Linux and similar
> systems and wondered what ``cd ""'' will do.

It's unspecified in the current POSIX edition.

Using the POSIX algorithm, the results depend on $CDPATH and $PWD.

> And now the behavior of the Bash. I tried these versions:
>
>      GNU bash, version 4.2.46(2)-release (x86_64-redhat-linux-gnu)
>      GNU bash, version 5.1.8(1)-release (x86_64-unknown-freebsd13.0)
>      GNU bash, version 5.1.16(1)-release (x86_64-pc-linux-gnu)
>      GNU bash, version 5.2.15(1)-release (x86_64-pc-linux-gnu)
>      GNU bash, version 5.2.21(1)-release (x86_64-pc-linux-gnu)
>      GNU bash, version 5.2.26(0)-release (amd64-portbld-freebsd13.2)
>
> The behavior is the same as for the zsh. It simply leaves the working
> directory unchanged.

That's the result of this step in the POSIX algorithm (`curpath' is the
empty string argument):

"If curpath does not begin with a <slash> character, set curpath to the 
string formed by the concatenation of the value of PWD, a <slash> character 
if the value of PWD did not end with a <slash> character, and curpath."

https://pubs.opengroup.org/onlinepubs/9699919799/utilities/cd.html#tag_20_14

> POSIX Programmer's Manual (cd(1p) manpage) says this:

I don't know what this is.

>        [9 unrelated special cases]

If that page is derived from the actual standard, the previous 9 steps are
decidedly not `unrelated special cases.'

>        10. The cd utility shall then perform actions equivalent to the
>             chdir() function called with curpath as the path argument. If
>             these actions fail for any reason, the cd utility shall
>             display an appropriate error message and the remainder of
>             this step shall not be executed. [...]
>
> So, it should do the same thing a chdir("").

It should not. It could do that if you used `cd -P ""' with CDPATH unset,
but you didn't.


> My opinion on this is that the ``cd ""'' command should fail with an
> error in this case. The zsh is the only POSIX-compatible or
> POSIX-shell-like shell that was available on machines to which I have
> access that exhibits this behavior.

The next edition of POSIX agrees with you.

> I propose to make Bash report an error when the user attempts to cd into
> empty string, possibly with an shopt option that allows changing
> behaviour of the cd back to the current one -- silently ignoring the
> command.

In POSIX mode, definitely, since POSIX will require it.

--
``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU    chet@case.edu    http://tiswww.cwru.edu/~chet/

OpenPGP_signature.asc
Description: OpenPGP digital signature