fix bugs

profile.d/rain.sh

@@ -300,7 +300,7 @@ _rain_engine()
             if ((100 * RANDOM / 32768 < falling_odd)); then
                 if ((++rains[idx + 1] > term_height)); then
                     rains=("${rains[@]:0:idx}" "${rains[@]:idx+num_rain_metadata:num_rains*num_rain_metadata}")
-                    ((num_rains--))
+                    num_rains=$(( num_rains - 1 ))
                     continue
                 fi
             fi
@@ -359,7 +359,7 @@ _rain_engine()
             X=$((term_width * RANDOM / 32768 + 1))
             Y=$((1 - drop_length))
             rains=("${rains[@]}" "$X" "$Y" "$rain_drop" "$drop_color" "$drop_length")
-            ((num_rains++))
+            num_rains=$(( num_rains + 1 ))
         fi
 
         do_render
@@ -684,7 +684,7 @@ rainbow()
         for ((col = 0; col < term_width; col++)); do
             idx=$((col - offset))
             while ((idx < 0)); do
-                ((idx += palette_width))
+                idx=$(( idx + palette_width ))
             done
             idx=$((idx % palette_width))
             row_line+="${RAINBOW_BG_PALETTE[idx]} "