fix blank variable when creating target

Allow passing prefix to limit pruning ops

README.md

@@ -51,11 +51,12 @@ AWS_S3_BUCKET_NAME="<xxx>"
 
 # **IMPORTANT, PLEASE READ THIS BEFORE USING THIS FEATURE**:
 # The mechanism used for pruning backups is not very sophisticated
-# and applies its rules to **all files in the target directory**,
+# and applies its rules to **all files in the target directory** by default,
 # which means that if you are storing your backups next to other files,
 # these might become subject to deletion too. When using this option
 # make sure the backup files are stored in a directory used exclusively
-# for storing them or you might lose data.
+# for storing them or to configure BACKUP_PRUNING_PREFIX to limit
+# removal to certain files.
 
 # Define this value to enable automatic pruning of old backups. The value
 # declares the number of days for which a backup is kept.
@@ -71,6 +72,15 @@ AWS_S3_BUCKET_NAME="<xxx>"
 
 # BACKUP_PRUNING_LEEWAY="10m"
 
+# In case your target bucket or directory contains other files than the ones
+# managed by this container, you can limit the scope of rotation by setting
+# a prefix value. This would usually be the non-parametrized part of your
+# BACKUP_FILENAME. E.g. if BACKUP_FILENAME is `db-backup-%Y-%m-%dT%H-%M-%S.tar.gz`,
+# you can set BACKUP_PRUNING_PREFIX to `db-backup-` and make sure
+# unrelated files are not affected.
+
+# BACKUP_PRUNING_PREFIX="backup-"
+
 ########### BACKUP ENCRYPTION
 
 # Backups can be encrypted using gpg in case a passphrase is given

src/backup.sh

@@ -105,6 +105,10 @@ echo "Will wait for next scheduled backup."
 
 prune () {
   target=$1
+  if [ ! -z "$BACKUP_PRUNING_PREFIX" ]; then
+    target="$target/${BACKUP_PRUNING_PREFIX}"
+  fi
+
   rule_applies_to=$(
     mc rm $MC_GLOBAL_OPTIONS --fake --recursive --force \
       --older-than "${BACKUP_RETENTION_DAYS}d" \
@@ -137,7 +141,7 @@ if [ ! -z "$BACKUP_RETENTION_DAYS" ]; then
   sleep "$BACKUP_PRUNING_LEEWAY"
   if [ ! -z "$AWS_S3_BUCKET_NAME" ]; then
     info "Pruning old backups from remote storage"
-    prune "backup-target/$bucket"
+    prune "backup-target/$AWS_S3_BUCKET_NAME"
   fi
   if [ -d "$BACKUP_ARCHIVE" ]; then
     info "Pruning old backups from local archive"

src/entrypoint.sh

@@ -17,6 +17,7 @@ BACKUP_ARCHIVE="${BACKUP_ARCHIVE:-/archive}"
 
 BACKUP_RETENTION_DAYS="${BACKUP_RETENTION_DAYS:-}"
 BACKUP_PRUNING_LEEWAY="${BACKUP_PRUNING_LEEWAY:-10m}"
+BACKUP_PRUNING_PREFIX="${BACKUP_PRUNING_PREFIX:-}"
 BACKUP_STOP_CONTAINER_LABEL="${BACKUP_STOP_CONTAINER_LABEL:-true}"
 
 AWS_S3_BUCKET_NAME="${AWS_S3_BUCKET_NAME:-}"