update help message and correctly set default backup location

lxc-backup.sh

@@ -8,18 +8,23 @@ main() {
         IFS="," read -r -a VM_FILTER <<< "$OPTARG"
         ;;
       d)
-        local backup_location="${OPTARG:-'.'}"
+        local backup_location="${OPTARG}"
         backup_location="${backup_location%/}"
         ;;
       t)
         declare -g TARGET="$OPTARG"
         ;;
+      h)
+        usage
+        ;;
       *)
         usage
         ;;
     esac
   done
 
+  backup_location=${backup_location:-$PWD}
+
   if [[ "${#VM_FILTER[*]}" -gt 0 ]]; then
     backup_vms "$backup_location" "${VM_FILTER[@]}"
   else
@@ -36,7 +41,19 @@ list_vms() {
 	lxc list -c n -f csv,noheader
 }
 
-usage() { echo "Usage: ${0##*/} [-l <vm[,vm...]>] [-d <backup_dir>] [-t <lxc|incus>]"; exit 1; }
+usage() {
+  cat <<EOF
+Usage: ${0##*/} [-l vm[,vm...]] [-d backup_dir] [-t lxc|incus] [-h]
+
+Options:
+  -l  Comma-separated list of VMs to back up
+  -d  Directory where backups will be stored (default: current directory)
+  -t  Manager type: lxc or incus (default: lxc)
+  -h  Show this message
+
+EOF
+  exit 1
+}
 
 backup_vms() {
   local backup_location="$1"; shift