+# atomically create file by command
+cmdsave = @echo $1 $2 \>$@; $1 $2 | sponge $@
+# download git checkout
+gitsave = @echo git pull or clone $@; \
+ [ -r $@/.git ] && cd $@ && git pull --ff-only || true; \
+ [ -e $@ ] || git clone "$1" $@
+
+sitemap.xml: tools/mksitemap
+ $(call cmdsave,$<)
+