hooks--update.sample: use hash-agnostic zero OID

Denton-L · gitster · commit d8d3d632f416 · 2020-09-23T09:31:45.000-07:00
The update sample hook has the zero OID hardcoded as 40 zeros. However,
with the introduction of SHA-256 support, this assumption no longer
holds true. Replace the hardcoded $z40 with a call to

	git hash-object --stdin &lt;/dev/null | tr '[0-9a-f]' '0'

so the sample hook becomes hash-agnostic.

Signed-off-by: Denton Liu &lt;liu.denton@gmail.com&gt;
Signed-off-by: Junio C Hamano &lt;gitster@pobox.com&gt;
diff --git a/templates/hooks--update.sample b/templates/hooks--update.sample
@@ -60,7 +60,7 @@ esac
 
 # --- Check types
 # if $newrev is 0000...0000, it's a commit to delete a ref.
-zero="0000000000000000000000000000000000000000"
+zero=$(git hash-object --stdin </dev/null | tr '[0-9a-f]' '0')
 if [ "$newrev" = "$zero" ]; then
 	newrev_type=delete
 else
