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

(+Brandon Williams, who may have more context for execvp-related things)

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?

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.