Use TextCrawler

TextCrawler is a free software with Search & Replace across files, insert or delete text. You can download from hereĀ

As mentioned on their website:

TextCrawler is a fantastic tool for anyone who works with text files. This powerful program enables you to instantly find and replace words and phrases across multiple files and folders. It utilises a flexible Regular Expression engine to enable you to create sophisticated searches, preview replace, perform batch operations, extract text from files and more. It is fast and easy to use, and as powerful as you need it to be.

I use this one to search a string of text to find out where it is across the whole folder and sometimes to batch replace.