On Tue, May 16, 2017 at 10:21:51AM -0700, Eric Rannaud wrote:
> On Tue, May 16, 2017 at 9:59 AM, Eric Rannaud <eric.rannaud@xxxxxxxxx> wrote:
> > When I use "git rebase --exec <cmd>" I'm basically writing a "foreach
> > commit in range { <cmd> }" in my shell. Same idea with git bisect run.
> >
> > A transparent optimization that tries execve() then falls back to the
> > user's shell sounds like a good idea.
>
> One issue with the execve-else-shell optimization is that sometimes a
> binary exists that will shadow an exported function or a shell
> builtin:
>
> git rebase --exec true master^^ # OK but in fact this runs /usr/bin/true
Yeah, this is the builtin thing I mentioned elsewhere. I think it's
pretty rare to run a builtin with no arguments and care about the
behavior differences.
> /usr/bin/time requires an argument. Even though the bash builtin time
> runs fine without argument.
>
> $ time
>
> real 0m0.000s
> user 0m0.000s
> sys 0m0.000s
I've run into the "time" distinction even when running things from the
shell, because the time builtin is special. E.g.:
$ time true
real 0m0.000s
user 0m0.000s
sys 0m0.000s
$ (echo foo | time true) 2>&1
0.00user 0.00system 0:00.00elapsed 0%CPU (0avgtext+0avgdata 1136maxresident)k
0inputs+0outputs (0major+61minor)pagefaults 0swaps
So to some degree, depending on builtins versus external commands
(especially when you're round-tripping through another program running a
second shell) is going to have some surprises.
> But if the optimization is applied to more complex commands, then we
> will have problems. For instance, the builtin echo supports \E, but
> /usr/bin/echo doesn't support it.
No, it shouldn't. If any of
|&;<>()$`\\\"' \t\n*?[#~=%
appear in the string, we always run the shell.
> In any case, the manpage says --exec <cmd> and "<cmd> will be
> interpreted as one or more shell commands.", it doesn't say "--exec
> <executable>".
Right, it's clearly supposed to use the shell, or behave as if the shell
were invoked (within reason).
-Peff