Splitting a CSV & keeping headers

csv-split.sh

#!/bin/bash

# file that needs to be split
filename="big_file.csv"
# directory for split files
split_dir="splits"
# string to prepend files 
split_prepend="small_file-"

# get the header from the first file
head -1 $filename > header.csv

# split the file into files with 100000 rows
split -l  100000 $filename ${split_dir}/${split_prepend}

# loop through split files & combine with header then clean up
for small_file in ${split_dir}/*
    do
        cat header.csv $small_file > $small_file.csv
        rm $small_file
    done

rm header.csv