Simple utility to split a single CSV into shards with header replicated in each of the outputs shards.
The tool produces shards in the same directory as the input CSV. For example,
/path/to/dir/input.csv produces /path/to/dir/input_shard_*.csv files.
It optionally takes the number of lines per shard as input. The default is 10000.
./split_csv.sh <csv_to_split> [num_lines_per_shard]