Need help understanding a back-up script
Need help understanding a back-up script
Hello everyone!
I had a container with a DB crap itself yesterday so I'm trying to speed up my learning to back up stuff.
I came across a script that taught me how to back-up a containerized postgres db at given intervals and it works. I managed to create db dumps and restore them. I've documented everything and now my whole docker-compose/env etc are on git control.
There's one part of the script I don't decypher but I'd like to maybe change it. It is about the number of back-up copies.
Here's the line from the tutorial:
ls -1 /backup/*.dump | head -n -2 | xargs rm -f
Can someone explain to me what this line does? I'd like to keep maybe 3 copies just in case the auto-backup backs up a rotten one.
Thanks!
Full code below:
backup: image: postgres:13 depends_on: - db_recipes volumes: - ./backup:/backup command: > bash -c "while true; do PGPASSWORD=$$POSTGRES_PASSWORD pg_dump -h db-postgresql -U $$POSTGRES_USER -Fc $$POSTGRES_DB > /backup/$$(date +%Y-%m-%d-%H-%M-%S).dump echo ""Backup done at $$(date +%Y-%m-%d_%H:%M:%S)"" ls -1 /backup/*.dump | head -n -2 | xargs rm -f sleep 86400 done"
This line seems to list all dumps and then deletes all but the two most recent ones.
In detail:
ls -1 /backup/*.dump
lists all files ending with .dump alphabetically inside the /backup directoryhead -n -2
returns all filenames except the two most recent ones from the end of the listxargs rm -f
passes the filenames torm -f
to delete themTake a look at explainshell.com.
I just looked up the man page, and actually
head -n -2
means "everything up to but not including the last two lines", so this should always leave two files remaining.You're right, I edited my comment. Thanks!