notmuch dump --format=batch-tag | sed 's/^.* -- /+common_tag -- /' | \
sort > EXPECTED
-notmuch dump --format=batch-tag | sed 's/^.* -- / -- /' | \
- notmuch restore --format=batch-tag
+notmuch dump --format=batch-tag | sed 's/^.* -- / -- /' > INTERMEDIATE_STEP
+notmuch restore --format=batch-tag < INTERMEDIATE_STEP
notmuch tag --batch < EXPECTED