Alex Chan wrote a 1000 word blog post about a 35 line python script to archive his Pinboard bookmarks.
Here’s what I’ve been using since I’ve started using Pinboard, which is close to Alex’s solution but only one line:
curl https://ME:[email protected]/v1/posts/all?format=json -o ~/Dropbox/pinboard-backups/pinboard-`date +%y%m%d`.json
This does not create separate yearly folders for the backups, and the output is in JSON, but those are easy changes if that’s your preference.
I have this set to run daily with a “@daily” crontab schedule.