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All source code in this repository was written by Miles B Huff, is Copyright (C) 2018 to him, and is licensed per the terms of the Lesser GNU General Public License v3.0+. The full terms of this license can be found at \Copyright.txt.

Most of 7-Zip is also licensed under the LGPL, albeit v2.1+, rather than v3.0+. The rest of 7-Zip is licensed under BSD3. Please see Archivers\7-Zip Copyright.txt for more info. Thanks for making such a great program, Igor Pavlov!

About

This repository contains a PowerShell script and the 64-bit PE binary of 7-Zip v18.05's CLI tool.

Said PowerShell script finds every .7z and .zip file in a given directory, and repacks them with a strong compression algorithm. This can save a few hundred megabytes in a power user's Downloads folder; but where it really shines, is when you use some sort of package manager or mod manager whose downloads use less-than-stellar compression strengths.

As a case-in-point, I ran this script on each folder in %appdata%\Roaming\Vortex\Downloads. My SkyrimSE folder (minus .rar files) went from 26.6GiBs, to 25.1GiBs -- a savings of 1.5GiBs, or about 6%! While 6% may not seem like much, there were several archives that were over 25% smaller after recompression. The reason the total number was 6% instead of 25%, is because most of that 26.6GiBs was [thankfully] already maximally compressed. Between Vortex's SkyrimSE and Skyrim downloads folders, and my user downloads folder, I saved probably about 2GiBs of space without deleting anything.

"Why would anyone ever use a weak compression algorithm?", you might be wondering. Well, there are actually times when a weaker compression algorithm is useful -- typically for data that needs to be accessed frequently (A really good example of a use-case for light compression, is transparent, partition-level compression.). But when you have a lot of archived data that you don't want to delete and that's mostly just collecting dust, repackaging it with a stronger compression algorithm can be a great thing to do.

Usage

Archive-Repacker.ps1 -Dir \path\ [-Pause|-Help]

• -Dir is where you specify a directory whose archives you'd like to repack.
• -Pause makes the script pause after each extraction. This can be very useful -- you can use this break period to run texture optimizers, for example. This can save you even more space.
• -Help prints help text.

If you don't know how to run PowerShell scripts, there are many tutorials out there on the Internet -- you need only search. One such tutorial may be found here: https://stackoverflow.com/questions/2035193/how-to-run-a-powershell-script.

Notes

If you're still using a 32-bit OS, you'll need to download a 32-bit version of 7z.exe. The latest can be found here: https://www.7-zip.org/download.html.

The way this script is currently configured, the contents of each archive will lose their modification dates. This gets a marginally better compression ratio. While this may be okay for end-users, it is not likely so for mod authors. If you are using this script to optimize your own archive, you can make it preserve modification dates by removing all instances of ,'-mtc-'.

If you would like to create archives with these settings without having to use this script, you can configure the 7-Zip File Manager to create just-as-strongly compressed archives. To do this, create a new archive, and use the following options:

• Archive format: .7z
• Compression level: Ultra
• Compression method: LZMA2
• Dictionary size: 128 MB (You may need to reduce this if you don't have much RAM. With a 128MB DS, I was using roughly 4GiBs of RAM for each large archive.) (Note that 128MB is the maximum for 32-bit computers.)
• Word size: 273 (Afaik, there's no reason not to use the maximum, here.)
• Solid Block size: Solid (This makes a huge difference.)

Request to Archive Creators

If you are creating an archive that you intend to ship over the Internet, please use a strong form of compression. Using weak compression algorithms (1) wastes bandwidth (This costs hosts and users alike extra money.), (2) makes downloads slower, and (3) wastes disk-space for both server hosts and end-users.

When creating archives, please do not use proprietary formats like .rar. These formats are (1) usually inferior in performance and compression ratios to Free/Libre formats like .7z, and (2) these formats cannot be created by Free/Libre archivers, like 7z. Moving everything to a standard of .7z or .zip on Windows will make everyone's lives easier.

Future Expansion

As I use Linux more often than Windows (at least at home), it's likely that I'll eventually make a bash version of this script. If and when I do, I might even try to get it on the AUR -- we'll just have to see. The bash version will likely support more compression algorithms than the PowerShell version, since I won't have to ship their binaries with the script.

I might add the option to only look at files modified after a certain date. This way, you can re-run the script on the same directory, without wasting time repacking already-optimized archives. This will require the removal of the -stl option, which sets the archive's modification date to that of its files.

This script is unlikely to gain support for .rar files. If I do ever add support, I will probably be unable to include the binary for the rar archiver, due to its proprietary license.