contrib/subtree: ensure only one rev is provided

While looking at the inline help for git-subtree.sh, I noticed that

	git subtree split --prefix=<prefix> <commit...>

was given as an option. However, it only really makes sense to provide
one revision because of the way the commits are forwarded to rev-parse
so change "<commit...>" to "<commit>" to reflect this. In addition,
check the arguments to ensure that only one rev is provided for all
subcommands that accept a commit.

Signed-off-by: Denton Liu <liu.denton@gmail.com>
Acked-by: Avery Pennarun <apenwarr@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/subtree/git-subtree.sh

@@ -14,7 +14,7 @@ git subtree add   --prefix=<prefix> <repository> <ref>
 git subtree merge --prefix=<prefix> <commit>
 git subtree pull  --prefix=<prefix> <repository> <ref>
 git subtree push  --prefix=<prefix> <repository> <ref>
-git subtree split --prefix=<prefix> <commit...>
+git subtree split --prefix=<prefix> <commit>
 --
 h,help        show the help
 q             quiet
@@ -77,6 +77,12 @@ assert () {
 	fi
 }
 
+ensure_single_rev () {
+	if test $# -ne 1
+	then
+		die "You must provide exactly one revision.  Got: '$@'"
+	fi
+}
 
 while test $# -gt 0
 do
@@ -185,6 +191,7 @@ if test "$command" != "pull" &&
 then
 	revs=$(git rev-parse $default --revs-only "$@") || exit $?
 	dirs=$(git rev-parse --no-revs --no-flags "$@") || exit $?
+	ensure_single_rev $revs
 	if test -n "$dirs"
 	then
 		die "Error: Use --prefix instead of bare filenames."
@@ -716,9 +723,8 @@ cmd_add_repository () {
 }
 
 cmd_add_commit () {
-	revs=$(git rev-parse $default --revs-only "$@") || exit $?
-	set -- $revs
-	rev="$1"
+	rev=$(git rev-parse $default --revs-only "$@") || exit $?
+	ensure_single_rev $rev
 
 	debug "Adding $dir as '$rev'..."
 	git read-tree --prefix="$dir" $rev || exit $?
@@ -817,16 +823,10 @@ cmd_split () {
 }
 
 cmd_merge () {
-	revs=$(git rev-parse $default --revs-only "$@") || exit $?
+	rev=$(git rev-parse $default --revs-only "$@") || exit $?
+	ensure_single_rev $rev
 	ensure_clean
 
-	set -- $revs
-	if test $# -ne 1
-	then
-		die "You must provide exactly one revision.  Got: '$revs'"
-	fi
-	rev="$1"
-
 	if test -n "$squash"
 	then
 		first_split="$(find_latest_squash "$dir")"