Invalid osmosis command when not filtering tags

[pnorman]

When not filtering by tags, the osmosis command consists of something like

osmosis \
--bounding-box top=41.2403 left=-117.27392 bottom=40.84965 right=-116.76519 \
--write-xml extract.osm

This is missing a line like --read-pbf $PBFFILE \

[pnorman]

note: also happens if not doing any filtering, suggesting

osmosis \
--write-xml extract.osm