split-csv-file.sh

#!/bin/bash

file_path='./your-file.csv'
n_lines=5000

# tail -n +2 $file_path: Prints the whole file starting from the second line (skip header)
# split -l $n_lines - part_: Split the content into small files of $n_lines each named "part_*"
tail -n +2 "${file_path}" | split -l "${n_lines}" - part_

# For each part_*
i=1
for part_x in part_*
do
  # Add the header to a temporary file
  head -n 1 "${file_path}" > tmp_file

  # Append part_x's content to the temporary file
  cat "${part_x}" >> tmp_file

  # Rename the temporary file and deletes part_x
  mv tmp_file "${file_path}.${i}"
  rm "${part_x}"

  i=$((i+1))
done