Here’s a simple script I put together to rotate backup files in a given directory with decreasing resolution the further away we get from the current time.

#!/bin/bash

set -euo pipefail

DRYRUN=${DRYRUN:-1}
DIR=${DIR:-'/backups/mysql'}
HOURS=${HOURS:-48}
DAYS=${DAYS:-35}
MONTHS=${MONTHS:-24}

usage() {
	echo "usage: DRYRUN=0 DIR=/backups HOURS=48 DAYS=30 MONTHS=24 $0"
	exit 1
}

if [ $DRYRUN -eq 1 ]; then
	echo "DRYRUN: No changes will be made"
fi

if [ "$HOURS" -lt 0 ] || [ "$DAYS" -lt 1 ] || [ "$MONTHS" -lt 1 ]; then
	echo "ERROR: Cannot have negative rotation"
	usage
fi

## Bail and cleanup if we exit early
cleanup() {
	find $DIR -type f -execdir rename 's/.process$//g' '{}' \;
}
trap cleanup EXIT
trap cleanup SIGINT

## Flag all the files for processing
find $DIR -type f | grep -v '.process$' | xargs -I{} mv {}{,.process}

while [ $MONTHS -gt 0 ]; do
	MONTHS=$(($MONTHS-1))
	days=$(( ( $(date '+%s') - $(date -d "$MONTHS months ago" '+%s') ) / 86400 ))
	file=$(find $DIR -type f -mtime "+$days" | sort -n | tail -n1)
	if [ "$DRYRUN" -eq 0 ]; then
		rename 's/.process$//g' "$file"
	else
		echo "MONTH:	$MONTHS	$file" | sed 's/.process$//'
	fi
done

while [ $DAYS -gt 0 ]; do
	DAYS=$(($DAYS-1))
	file=$(find $DIR -type f -mtime "+$DAYS" | sort -n | tail -n1)
	if [ "$DRYRUN" -eq 0 ]; then
		rename 's/.process$//g' "$file"
	else
		echo "DAY:	$DAYS	$file" | sed 's/.process$//'
	fi
done

while [ $HOURS -gt 0 ]; do
	HOURS=$(($HOURS-1))
	minutes=$(($HOURS*60))
	file=$(find $DIR -type f -mmin "+$minutes" | sort -n | tail -n1)
	if [ "$DRYRUN" -eq 0 ]; then
		rename 's/.process$//g' "$file"
	else
		echo "HOUR: 	$HOURS	$file" | sed 's/.process$//'
	fi
done

## Delete all remaining files
[ "$DRYRUN" -eq 0 ] && rm "$DIR"/*.process 2> /dev/null
Code language: Bash (bash)