A bash script that creates incremental backups of an SD card on macOS using rsync

m8-incremental-backup.sh

#!/bin/bash
#
# Incremental backup script for SD card on macOS with rotation
#

# === CONFIGURATION ===
SDCARD="/Volumes/M8"	                       # Mount point of the SD card
BACKUPDIR="$HOME/Backups/m8-sd-backups"      # Where backups are stored
DATE=$(date +%Y-%m-%d-%H%M%S)                # Timestamp for snapshot folder
DEST="$BACKUPDIR/backup-$DATE"               # New backup folder
LATEST="$BACKUPDIR/latest"                   # Symlink to last backup
KEEP=5                                       # Number of backups to keep

# === CHECKS ===
if [ ! -d "$SDCARD" ]; then
    echo "Error: SD card not mounted at $SDCARD"
    exit 1
fi

echo "$(date): Starting backup of $SDCARD to $DEST"

mkdir -p "$BACKUPDIR"

# === RSYNC BACKUP ===
if [ -d "$LATEST" ]; then
    rsync -a --delete --link-dest="$LATEST" --progress "$SDCARD/" "$DEST/"
else
    rsync -a --delete --progress "$SDCARD/" "$DEST/"
fi

# === UPDATE SYMLINK ===
rm -f "$LATEST"
ln -s "$DEST" "$LATEST"

if [ $? -eq 0 ]; then
    echo "Backup completed successfully"
else
    echo "Backup encountered an error, check the logs for details"
    exit 1
fi

# === ROTATE OLD BACKUPS ===
cd "$BACKUPDIR" || exit 1
BACKUPS=(backup-*)
COUNT=${#BACKUPS[@]}

if [ "$COUNT" -gt "$KEEP" ]; then
    REMOVE=$((COUNT - KEEP))
    echo "Removing $REMOVE old backup(s)..."
    for OLD in "${BACKUPS[@]:0:$REMOVE}"; do
        rm -rf "$OLD"
        echo "Deleted $OLD"
    done
fi