Rename multiply files

#!/usr/bin/env bash

search_dir="../Pictures/untitled_folder"

for file in "$search_dir"/*
do
  date_transfer=$(stat -f '%Sm' "$file")
  filename=$(basename "$file")
  extension="${filename##*.}"
  new_name="$(date -j -f '%b %d %T %Y' "$date_transfer" '+%Y-%m-%d %H.%M.%S').$extension"
  if [ -f "$file" ]
    then
      mv "$file" "$search_dir/$new_name"
      echo "Renamed from: $file to: $search_dir/$new_name"
  fi
done