# The following will split a CSV (file.csv) into multiple parts of 1 million lines each
# with each part having its own header.
#
# PREFIX denotes the filename to use for the parts.  A number will be added to the end.

tail -n +2 file.csv |
split -d -l 1000000 - --filter='sh -c "{ head -n1 file.csv; cat; } > $FILE"' PREFIX