I've broken my Arch installation more times than I can remember, usually interrupting pacman on accident. Recently I had some more serious corruption occur so the only real choice I had was to reinstall everything since I had at least 30+ packages break and I didn't have time to figure out what was going on exactly.

Below is the script I used to reinstall everything.

#!/bin/bash
pacman -Sy
packages=($(comm -12 <(pacman -Slq|sort -u) <(pacman -Qq|sort -u)))
pacman -S --overwrite "*" $(echo ${packages[@]} | tr '\n' ' ')

Important Notes

Once you reinstall, some things may break, check for the following:

• Reconfigure your enabled locales, refer to the Arch installation guide.

Explanation

First of all, we need to update the package database so that we stay up to date. You should do this in order to avoid 404 errors from mirrors and to stay up to date on the latest packages.

pacman -Sy

Next, we take all of the installed packages and compare them to pacman's database, this is to filter out any packages which you may have installed from AUR (i.e. using paru) or other places which you can't reinstall using pacman. You could modify this script to instead grab all installed packages and feed them into your AUR helper, but I would rather get into my system as soon as possible and only then update my AUR packages.

packages=($(comm -12 <(pacman -Slq|sort -u) <(pacman -Qq|sort -u)))

The previous instruction outputs all the packages separated by a newline, so we need to convert this newline to a space and then we can feed it into pacman. We also specify --overwrite "*" which tells pacman to overwrite any existing files (which would probably be present if you interrupted pacman previously) and would cause the installation to fail.

pacman -S --overwrite "*" $(echo ${packages[@]} | tr '\n' ' ')

And that's pretty much it, I wrote this just to have a reference for the future but it might help someone else.