Title: How to split a file into small parts

	Title: How to split a file into small parts
	Author: Solène
	Date: 21 March 2021
	Tags: openbsd unix
	Description:

	# Introduction

	Today I will present the userland program "split" that is used to split
	a single file into smaller files.

	OpenBSD split(1) manual page

	# Use case

	Split will create new files from a single files, but smaller. The
	original file can be get back using the command cat on all the small
	files (in the correct order) to recreate the original file.

	There are several use cases for this:

	- store a single file (like a backup) on multiple medias (floppies,
	700MB CD, DVDs etc..)
	- parallelize a file process, for example: split a huge log file into
	small parts to run analysis on each part
	- distribute a file across a few people (I have no idea about the use
	but I like the idea)

	# Usage

	Its usage is very simple, run split on a file or feed its standard
	input, it will create 1000 lines long files by default. -b could be
	used to tell a size in kB or MB for the new files or use -l to change
	the default 1000 lines. Split can also create a new file each time a
	line match a regex given with -p.

	Here is a simple example splitting a file into 1300kB parts and then
	reassemble the file from the parts, using sha256 to compare checksum of
	the original and reconstructed files.

	```split and reassemble example
	solene@kongroo ~/V/pmenu> split -b 1300k pmenu.mp4
	solene@kongroo ~/V/pmenu> ls
	pmenu.mp4 xab xad xaf xah xaj xal xan
	xaa xac xae xag xai xak xam
	solene@kongroo ~/V/pmenu> cat x* > concat.mp4
	solene@kongroo ~/V/pmenu> sha256 pmenu.mp4 concat.mp4
	SHA256 (pmenu.mp4) = e284da1bf8e98226dc78836dd71e7dfe4c3eb9c4172861bafcb1e2afb…
	SHA256 (concat.mp4) = e284da1bf8e98226dc78836dd71e7dfe4c3eb9c4172861bafcb1e2afb…
	solene@kongroo ~/V/pmenu> ls -l x*
	-rw-r--r-- 1 solene wheel 1331200 Mar 21 16:50 xaa
	-rw-r--r-- 1 solene wheel 1331200 Mar 21 16:50 xab
	-rw-r--r-- 1 solene wheel 1331200 Mar 21 16:50 xac
	-rw-r--r-- 1 solene wheel 1331200 Mar 21 16:50 xad
	-rw-r--r-- 1 solene wheel 1331200 Mar 21 16:50 xae
	-rw-r--r-- 1 solene wheel 1331200 Mar 21 16:50 xaf
	-rw-r--r-- 1 solene wheel 1331200 Mar 21 16:50 xag
	-rw-r--r-- 1 solene wheel 1331200 Mar 21 16:50 xah
	-rw-r--r-- 1 solene wheel 1331200 Mar 21 16:50 xai
	-rw-r--r-- 1 solene wheel 1331200 Mar 21 16:50 xaj
	-rw-r--r-- 1 solene wheel 1331200 Mar 21 16:50 xak
	-rw-r--r-- 1 solene wheel 1331200 Mar 21 16:50 xal
	-rw-r--r-- 1 solene wheel 1331200 Mar 21 16:50 xam
	-rw-r--r-- 1 solene wheel 810887 Mar 21 16:50 xan
	```

	# Conclusion

	If you ever need to split files into small parts, think about the
	command split.

	For more advanced splitting requirements, the program csplit can be
	used, I won't cover it here but I recommend reading the manual page for
	its usage.

	csplit manual page