-rm -f .git/MERGE_HEAD .git/ORIG_HEAD
-echo $head > .git/ORIG_HEAD
-echo $merge > .git/MERGE_HEAD
+: ${GIT_DIR=.git}
+: ${GIT_OBJECT_DIRECTORY="${SHA1_FILE_DIRECTORY-"$GIT_DIR/objects"}"}
+
+rm -f "$GIT_DIR"/MERGE_HEAD "$GIT_DIR"/ORIG_HEAD
+echo $head > "$GIT_DIR"/ORIG_HEAD
+echo $merge > "$GIT_DIR"/MERGE_HEAD