Download the "Scripts for automatic map sync" based on your operating system:
If you're using Windows, download the .bat file.
If you're using Linux, download the .sh file.
Run the script:
If you're on Windows, Windows Defender SmartScreen may display a warning prompt asking if you want to run the file. Rest assured, it's safe — simply choose "Run anyway" to proceed.
The add-on maps will be updated in your game directory:
The script will automatically download any missing add-on maps and update any outdated ones from its list.
During this process, any add-ons that are not part of the update will be disabled.
After the script completes, you’ll need to manually re-enable these add-ons in the in-game "Add-ons" page.
Credits: A huge thanks to sheo for developing and maintaining the scripts and the add-on maps download list, as well as running L4D2Center.