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Re: git rebase regression: cannot pass a shell expression directly to --exec




On Tue, May 16, 2017 at 09:41:24AM -0700, Jonathan Nieder wrote:

> Jeff King wrote:
> > On Mon, May 15, 2017 at 11:25:03PM -0400, Jeff King wrote:
> 
> >> One hack would be to look for BASH_FUNC_* in the environment and disable
> >> the optimization in that case. I think that would make your case Just
> >> Work. It doesn't help other oddball cases, like:
> >>
> >>   - you're trying to run a shell builtin that behaves differently than
> >>     its exec-able counterpart
> >>
> >>   - your shell has some other mechanism for defining commands that we
> >>     would not find via exec. I don't know of one offhand. Obviously $ENV
> >>     could point to a file which defines some, but for most shells would
> >>     not read any startup files for a non-interactive "sh -c" invocation.
> >
> > So I was thinking something like the patch below, though I guess
> > technically you could look for BASH_FUNC_$argv[0]%%, which seems to be
> > bash's magic variable name. I hate to get too intimate with those
> > details, though.
> >
> > Another option is to speculatively run "foo" without the shell, and if
> > execve fails to find it, then fall back to running the shell. That would
> > catch any number of cases where the shell "somehow" finds a command that
> > we can't.
> 
> Hm.  execvp explicitly does this when it hits ENOEXEC, but not for
> ENOENT.  Do you know why that is?

When execvp(foo) falls back on ENOEXEC, it is not running "sh -c foo".
It is actually running "sh foo" to run the script contents. So it's
about letting you do:

  echo "no shebang line" >script
  chmod +x script
  ./script

And nothing to do with shell builtins.

> I think we want to behave consistently for shell builtins and for
> exported functions --- they are different sides of the same problem,
> and behaving differently between the two feels confusing.

Yes, I think ideally we'd handle it all transparently. Although I'd also
point out that Git the behavior under discussion dates back to 2009 and
this is (as far as I can recall) the first report. So documenting the
current behavior might not be that bad an option.

-Peff