A hastily and poorly written bash script. These days I start every bash script with what I now think of as the "Brexit Options":

  set -eu; set -o pipefail

The key missing one in this case was `-u`. That stops the script if you have an unset variable.

This script would do some stuff, and put a new website in place, and then remove the old one. So, my bash script had the line:

  rm -rf /var/www/$olddir

You can see it already. I ran it with $olddir unset. I think I had it in my head that the directory would simply not be found so that was fine. For those of you unfamiliar with bash, since olddir="", what actually ran was:

  rm -rf /var/www/

Gigabytes lost (back then, a GB was a lot!). We had backups but they took hours to restore. Horrible, horrible day.