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Re: Possible Bug in command and type posix compliance


From: Michael S
Subject: Re: Possible Bug in command and type posix compliance
Date: Fri, 5 Apr 2019 19:40:25 -0400

That sound like a good solution to me as having a program in your hash
table that isn't executable isn't much of an advantage anyway and it's
desirable to search the whole PATH again to find a command that is
executable. I found where it's adding to the hash table in findcmd.c and
I'll add some additional logic to not add to the hash table in this case.

Thanks,

On Fri, Apr 5, 2019 at 11:00 AM Chet Ramey <address@hidden> wrote:

> On 4/5/19 2:28 AM, Michael S wrote:
> > Hello,
> >
> > I believe I have found a bug when using the posix compliant bash. From
> this
> > page point 53
> > https://www.gnu.org/software/bash/manual/html_node/Bash-POSIX-Mode.html
> it
> > states that type and command should not return a binary that is non
> > executable. For most cases this is currently true and the check when
> > searching the patch ensures this in type.def. However in the case that
> the
> > user has tried to execute the program and the command has been added to
> > that hash table the check fails.
>
> It's not clear that this is a POSIX conformance problem. Behavior varies.
> Bash and ash-derived shells (dash/*BSD sh) behave as you observed, ksh-like
> shells (ksh93, mksh) don't fall back to files without the excute bit set in
> $PATH or put these `non-executables' into the hash table.
>
> The issue is that POSIX makes it clear that the only way to determine
> whether or not a file is an executable file is to try and execute it. By
> the time that happens, you're running in a subshell and it's too late to
> do anything about the parent's command hash table.
>
> Maybe the best thing to do is not to insert a command from $PATH that
> doesn't have the execute bit set into the hash table, but still return
> it as the fallback possibility to attempt for execution.
>
> Chet
> --
> ``The lyf so short, the craft so long to lerne.'' - Chaucer
>                  ``Ars longa, vita brevis'' - Hippocrates
> Chet Ramey, UTech, CWRU    address@hidden    http://tiswww.cwru.edu/~chet/
>


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