Add new condition for when not removing any backups

Add a check for when retention equals 0. When retentions is set to 0 but no backups exist the message would still say "No old backups to remove for $vm".

This change changes the message as no backups would be removed even if they were found.

lxc-backup.sh

@@ -52,7 +52,7 @@ Options:
   -d  Directory where backups will be stored (default: current directory)
   -t  Manager type: lxc or incus (default: lxc)
   -x  Compression algorithm (e.g. gzip, zstd, none)
-  -c  Cleanup old backups keeping a set number (default: 2)
+  -c  Cleanup old backups and keep last <n> (default: keep all)
   -h  Show this message
 EOF
   exit 1
@@ -64,7 +64,7 @@ start_backup() {
   local compression="$3"
   local ext=".${compression}"
 
-  if [[ "$compression" == 'none' ]]; then 
+  if [[ "$compression" == 'none' ]]; then
     ext=""
   else
     command -v "$compression" >/dev/null 2>&1 || { echo "$compression command not found"; exit 1; }
@@ -86,10 +86,12 @@ prune_backups() {
   local backup_dir="$2"
   local retention="$3"
   mapfile -t backup_files < <(find "${backup_dir}/${vm}" -maxdepth 1 -type f -printf '%T@ %p\n' | sort -n | head -n "-${retention}" | cut -d' ' -f2-)
-  
+
   if [[ ${#backup_files[@]} -gt 0 ]]; then
     echo "Removing ${#backup_files[@]} old backup files for $vm (keeping last $retention files)"
     printf '%s\0' "${backup_files[@]}" | xargs -0 rm -fv > /dev/null
+  elif [[ "${retention}" -eq 0 ]]; then
+    echo "Keeping all existing backups for $vm"
   else
     echo "No old backups to remove for $vm"
   fi