Splitting a CSV file into multiple files (using Mac Terminal)

split_csv.sh

# to split the file
split -l 100000 -d filename.csv file_

# to add the csv extension to each of the files
for i in $(find file_*); do mv $i "$i.csv"; done

# to put the header from the first file into each of the other files
for i in $(find . -type f -name "file_*.csv" -not -name "file_00.csv");
    do echo -e "$(head -1 file_00.csv)\n$(cat $i)" > $i;
done