fix some incorrect variable names

lxc-backup.sh

@@ -17,10 +17,10 @@ main() {
       x)
         declare -g EXTENSION
         if [[ "${OPTARG,,}" == 'none' ]]; then
-          EXTENTION=""
+          EXTENSION=""
         else
           command -v "$OPTARG" >/dev/null 2>&1 || { echo "$OPTARG command not found"; exit 1; }
-          EXTENTION="${OPTARG,,}"
+          EXTENSION="${OPTARG,,}"
         fi
 
         declare -g COMPRESSION="$OPTARG"
@@ -91,9 +91,11 @@ start_backup() {
   local vm=$1
   local backup_base="$2"
   local compression="${COMPRESSION:-none}"
-  local ext="${EXTENTION}" ; [[ -n "$ext" ]] && ext=".${ext}"
+  local ext="${EXTENSION}" ; [[ -n "$ext" ]] && ext=".${ext}"
   local destination="${backup_base}/${vm}"
-  local backup_name="${vm}_$(date +"%Y-%m-%d_%H-%M-%S").tar${ext}"
+
+  local backup_name
+  backup_name="${vm}_$(date +"%Y-%m-%d_%H-%M-%S").tar${ext}"
 
   [[ -d "$backup_base" ]] || { echo "${backup_base} is not a directory"; exit 1; }
   [[ -d "$destination" ]] || mkdir "$destination"
@@ -109,7 +111,7 @@ prune_backups() {
   mapfile -t backup_files < <(find "$backup_directory" -maxdepth 1 -type f -printf '%T@ %p\n' | sort -n | head -n "-${files_to_keep}" | cut -d' ' -f2-)
   
   if [[ ${#backup_files[@]} -gt 0 ]]; then
-    echo "Removing ${#qcow2_files[@]} old backup files for $vm (keeping last $total_files_to_keep files)"
+    echo "Removing ${#backup_files[@]} old backup files for $vm (keeping last $files_to_keep files)"
     printf '%s\0' "${backup_files[@]}" | xargs -0 rm -fv
   else
     echo "No old backups to remove for $vm"