[Toybox] Questions about realpath -s

[enh]

i've not used either option personally, so i have no opinion either, and
would default to "whichever's easier until proven otherwise". (and there is
no realpath(1) on macOS, so no second opinion from that direction either.)

the specific `realpath --relative-to` request i've seen was specifically
for the kernel's CONFIG_IKHEADERS option, though there are a handful of
uses in the AOSP tree too.

uses of `realpath --no-symlinks` just seems to be a few "random" use cases.
i think they're just to make the path more readable for humans!

On Sun, Jul 25, 2021 at 4:05 AM Rob Landley <rob at landley.net> wrote:

> You asked about:
>
> > On 7/23/21 4:26 PM, enh wrote:
> >>   realpath (-s (--no-symlinks), --relative-to)
> >
>
> Do you want the exact behavior of the gnu one, or do you want consistent
> behavior? Because:
>
>   $ ls -l Xilinx
>   lrwxrwxrwx 1 landley landley 10 Dec 13  2019 Xilinx -> old/Xilinx
>   $ realpath Xilinx/..
>   /home/landley/old
>   $ realpath -s Xilinx/..
>   /home/landley
>   $ cd Xilinx
>   $ realpath ..
>   /home/landley/old
>   $ realpath -s ..
>   /home/landley/old
>
> Is inconsistent in how it treats the path supplied on the command line (may
> contain symblinks) and the path to the current directory (readlink -f).
>
> I _think_ realpath -s should use $PWD as the "path to this point" instead
> of
> getcwd(), because we may have traversed symlinks to get here and realpath
> -s
> seems to be trying to do the "cd .." thing where .. unravels $PWD instead
> of
> resolving ".." to navigate up the actual filesystem hierarchy...
>
> But that's not what the gnu one is doing? The gnu one is doing one thing
> when
> the .. eats a directory we just supplied, and a different thing when ..
> eats a
> directory we're in, even WHEN the directory we're in is a symlink and we
> can
> tell that because the shell exports $PWD. In fact:
>
>   $ env -i bash -c env
>   PWD=/home/landley/old/Xilinx
>   SHLVL=0
>   _=/usr/bin/env
>
> PWD is one of three variables exported by default into an empty
> environment.
> (And I can always fall back to getcwd() if $PWD isn't set, or if I'm
> feeling
> fancy if it doesn't stat equal to ".")
>
> Also:
>
>   $ realpath -s doesnotexist/..
>   realpath: doesnotexist/..: No such file or directory
>
> (See also "realpath -s really can't cope when cwd has been deleted".)
>
> It would be nice if there was a specification for this...
>
> Rob
>
> P.S. Busybox realpath doesn't have -s, so I haven't got a second opinion
> here.
>
> P.P.S. This:
>
>   $ realpath -s Xilinx/14.7/../..
>   /home/landley
>   $ realpath --relative-to Xilinx -s Xilinx/14.7/../..
>   ..
>
> Makes me sad, but I suppose what it asked for is "the relative path you
> feed to
> cd to get there"...
>
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