#!/bin/bash

if test "${#}" -ne 2; then
    printf "%s\n" \
        "split file into N parts" \
        "usage: $(basename $0) <file.txt> <parts>"
    exit 1
fi

if ! command -v split &>/dev/null; then
    printf "%s\n" "split not found"
    exit 1
fi

file="${1}"
parts="${2}"
filename="${file%.*}"
extension="${file##*.}"
total_lines=$(wc -l < "${file}")
lines_per_part=$((total_lines / parts + 1))
split -l "${lines_per_part}" -d --additional-suffix=".${extension}" "${file}" "${filename}_"