Windows – Search and replace tool that can handle multiple files and subfolders

I’m looking for a tool which can search/replace within file contents for a broad range of file types (i.e. it should, if possible,  process the maximum possible number of file types like .txt, .sql, .xls, .doc, .r, .c, etc.). It should handle multiple files in multiple folders/subfolders. Just searching the file contents is not enough for me, it should also have the replacing capability.

Solution:

grepWin (not to be confused with Windows Grep) can do this. It supports text-based search and replace, as well as regular expression search and replace:

grepWin is free and open source.