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

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.

You'd still have confusing behavior if your shell builtin behaved
differently than the exec-able version, though (because we'd quietly use
the exec-able one), but I would imagine that's exceedingly rare.

I dunno. Maybe the whole thing is a fool's errand.

diff --git a/run-command.c b/run-command.c
index 1c02bfb2e..8328d27fb 100644
--- a/run-command.c
+++ b/run-command.c
@@ -240,12 +240,24 @@ int sane_execvp(const char *file, char * const argv[])
 	return -1;
+static int env_has_bash_functions(void)
+	extern char **environ;
+	char **key;
+	for (key = environ; *key; key++)
+		if (starts_with(*key, "BASH_FUNC_"))
+			return 1;
+	return 0;
 static const char **prepare_shell_cmd(struct argv_array *out, const char **argv)
 	if (!argv[0])
 		die("BUG: shell command is empty");
-	if (strcspn(argv[0], "|&;<>()$`\\\"' \t\n*?[#~=%") != strlen(argv[0])) {
+	if (strcspn(argv[0], "|&;<>()$`\\\"' \t\n*?[#~=%") != strlen(argv[0]) ||
+	    env_has_bash_functions()) {
 		argv_array_push(out, SHELL_PATH);