Check if old ascii link in cache exists before trying to create it

scripts/archive_tower.sh

@@ -36,8 +36,11 @@ fi
     year=${DATE:0:4}
     month=${DATE:4:2}
     day=${DATE:6:2}
-    mkdir -p $TOWER_CACHE_DIR/ascii/${year}/${month}/
-    ln -s "$TOWER_PRAW_DIR/${year}/${month}/${day}/rig_tower.${year}-${month}-${day}.ascii" "$TOWER_CACHE_DIR/ascii/${year}/${month}/"
+    link_fn="$TOWER_CACHE_DIR/ascii/${year}/${month}/rig_tower.${year}-${month}-${day}.ascii"
+    if [ ! -e $link_fn ]; then
+        mkdir -p $TOWER_CACHE_DIR/ascii/${year}/${month}/
+        ln -s "$TOWER_PRAW_DIR/${year}/${month}/${day}/rig_tower.${year}-${month}-${day}.ascii" ${link_fn}
+    fi
 
     log_info "Done"