[Toybox] Add remaining pwd options

[Felix Janda]

On 12/30/12 at 04:43am, Rob Landley wrote:
> On 12/29/2012 07:38:24 AM, Felix Janda wrote:
> > POSIX says that "pwd" should behave the same as "pwd -L". The current
> > "pwd -P" should behave the same way as the previous version of "pwd".  
> > It
> > just returns the getcwd() output. "pwd -L" does just check whether the
> > environment variable PWD is also a valid current working directory and
> > uses that instead of the output of getcwd() if that's the case.
> 
> Here's a fun corner case:
> 
>    $ cd
>    $ mkdir fruit
>    $ cd fruit
>    $ (cd .. && rmdir fruit)
>    $ ls -l
>    total 0
>    $ pwd
>    /home/landley/fruit
>    $ pwd -L
>    /home/landley/fruit
>    $ pwd -P
>    pwd: error retrieving current directory: getcwd: cannot access parent
>    directories: No such file or directory
>    $ pwd -L
>    pwd: error retrieving current directory: getcwd: cannot access parent
>    directories: No such file or directory
>    $ pwd
>    pwd: error retrieving current directory: getcwd: cannot access parent
>    directories: No such file or directory
> 
> The amount of magic inherent in that behavior is kind of mind-boggling.  
> If you can't getcwd() then it's happy printing $PWD, until you call pwd  
> -P and that somehow invalidates $PWD? (Which means pwd is totally a  
> shell builtin because a child process can't persistently set an  
> environment variable in the parent process).

POSIX contains many surprises. In the section on environment variables it
says that $PWD should be set if "pwd -P" was specified. What happens if an
error happens seems unspecified.

> Sigh. And the whole "PWD defaults to -P unless POSIXLY_CORRECT" thing  
> above: while I'm sure that code is in there, it's not actually what  
> it's doing here. Because GNU code is INSANE, and someone somewhere  
> thought this tangle of corner cases might help somehow.
> 
> Right, in the case of a deleted directory $PWD is all we've got, so  
> have -L (which is the default) print it but first validate it's an  
> absolute path with no .. in it. Only validate that current directory  
> and path directory point to the same place if there IS a current  
> directory. If that's not what they want, -P exists.

In the corner case shouldn't pwd (-L and -P) just give an error message?
($PWD does not contain an absolute pathname of the current working
directory.)

Felix

> Rob

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