Re: [PATCH] Work around ash "alternate value" expansion bug

From: Junio C Hamano <gitster@pobox.com>
Date: Apr 18, 2009, 18:30 UTC
Message-ID: <7vfxg5x199.fsf@gitster.siamese.dyndns.org>
In-Reply-To: <1240044459-57227-1-git-send-email-ben@ben.com>

Ben Jackson <ben@ben.com> writes:

Show 54 quoted lines

> Ash (used as /bin/sh on many distros) has a shell expansion bug
> for the form ${var:+word word}.  The result is a single argument
> "word word".  Work around by using ${var:+word} ${var:+word} or
> equivalent.
>
> Signed-off-by: Ben Jackson <ben@ben.com>
> ---
>
> I found this by accident while testing another trivial git-am patch.
> It was broken about a week ago in git-am.sh by f79d4c8a and one of the
> test cases caught it on FreeBSD.
>
> The other instance has been around longer and I found it by grepping.
> I added a new testcase (none too exciting) which exposes the problem.
> There are more instances of ${x:+alt} which don't have spaces which I
> did not touch.
>
> For the curious:
>
> bash on linux:
> 	$ parent=ok
> 	$ echo ${parent:+-p $parent}
> 	-p ok
> 	$ for i in ${parent:+-p $parent} ; do echo .$i; done
> 	.-p
> 	.ok
>
> ash (/bin/sh) on freebsd:
> 	$ parent=ok
> 	$ echo ${parent:+-p $parent}
> 	-p ok
> 	$ for i in ${parent:+-p $parent} ; do echo .$i; done
> 	.-p ok
>
> This is probably a bug in ash.  It does expand ${foo:+*} into many words.
>
>  git-am.sh                  |    2 +-
>  git-submodule.sh           |    2 +-
>  t/t7400-submodule-basic.sh |    8 ++++++++
>  3 files changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/git-am.sh b/git-am.sh
> index bfc50c9..e539c60 100755
> --- a/git-am.sh
> +++ b/git-am.sh
> @@ -570,7 +570,7 @@ do
>  			GIT_COMMITTER_DATE="$GIT_AUTHOR_DATE"
>  			export GIT_COMMITTER_DATE
>  		fi &&
> -		git commit-tree $tree ${parent:+-p $parent} <"$dotest/final-commit"
> +		git commit-tree $tree ${parent:+-p} $parent <"$dotest/final-commit"
>  	) &&
>  	git update-ref -m "$GIT_REFLOG_ACTION: $FIRSTLINE" HEAD $commit $parent ||
>  	stop_here $this

I do not mind this one, but

Show 10 quoted lines

> diff --git a/git-submodule.sh b/git-submodule.sh
> index 7c2e060..bb3766d 100755
> --- a/git-submodule.sh
> +++ b/git-submodule.sh
> @@ -204,7 +204,7 @@ cmd_add()
>  	else
>  
>  		module_clone "$path" "$realrepo" || exit
> -		(unset GIT_DIR; cd "$path" && git checkout -f -q ${branch:+-b "$branch" "origin/$branch"}) ||
> +		(unset GIT_DIR; cd "$path" && git checkout -f -q ${branch:+-b} ${branch:+"$branch"} ${branch:+"origin/$branch"}) ||

this is too ugly to live in our codebase, and without an accompanying code comment, I am sure somebody (if not myself) will "fix" it again.

	(
        	unset GIT_DIR
		cd "$path" &&
		# BSD ash mishandles ${branch:+-b "$branch" ...}, sheesh.
                case "$branch" in
                '')	git checkout -f -q ;;
                ?*)	git checkout -f -q -b "$branch" "origin/$branch" ;;
                esac
	) ||
	...