On 01/10/2013 02:25:13 PM, Felix Janda wrote:
On 01/02/13 at 12:41am, Rob Landley wrote:
> What I did was disable #3 in the case where cwd doesn't exist. So
the
> new rule #3 is:
>
> 3) If cwd exists and $PWD doesn't point to it, fall back to -P.
Thanks for the clarification.
Your version of 3) depends on whether pwd is builtin or not. Do you
mean
something like "If getcwd() fails ..."?
cwd is what getcwd() returns. $PWD is an environment variable.
> > BTW, in the case that one has deleted and recreated one's current
> > working
> > directory one could also use "cd ." to get to the new directory.
>
> Good to know. (This means the shell is special casing "." as well as
> "..". I need to read the susv4 shell stuff thoroughly, it's been
> years...)
The susv4 page special cases "." and ".." a bit, but it seems to me
only
in the $CDPATH handling. Ah, I see that you don't care about $CDPATH
from
the about page.
$CDPATH and $PWD are separate.
Then I think one can leave out step 5 on susv4's page on
cd, and "cd ." is no more special than "cd dir"; it does a chdir to
"$PWD/."
or "$PWD/dir" respectively and then updates $PWD to its canonical
form. (and
modifies $OLDPWD also if necessary)
Um, steps 4 and 8 are the ones that say cd . and .. are special?
Another interesting situation is if your current directory "/dir" has
been
moved to "/olddir" and say "/dir" has been recreated. Then "cd ."
will move
you to new directory whereas "cd $(pwd -P)" will preserve your cwd
and fix up
$PWD. (at least for a shell behaving posixly correct)
Preserving the cwd is what I wanted to do, yes.
Imagine the same situation but with "/dir" not being recreated after
being
moved. Then "cd ." should fail according to susv4 since "$PWD/." =
"/dir/.",
which does not exist. Would you like to have "cd ." behave the same as
"cd $(pwd)" in this case? Bash does this if not in POSIX mode.
Busybox ash
doesn't do this and for some reason even "cd $(pwd)" fails.
I want the great mass of existing shell scripts to work, which means
reproducing historical behavior. Posix is (mostly) a reasonable
consensus documentation of historical behavior.
Felix
Rob
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