InFile Seeker is a free tool which can search vast numbers of text files for the keywords you need.

The program is compact, under 400KB, and runs without installation on anything from Windows 2000 up.

The search procedure works much as you'd expect. Specify a starting folder, the file types to search, enter a keyword and you're ready to go.

InFile Seeker displays any hits in the "Seeking results" tab. There's a list of files, selecting any of these displays it contents with the search keywords highlighted, and you can open the file (or its containing folder) with a click.

Version 1.8:
 

• Added support for Windows 10;
• Added a menu to open files with their default application, Notepad or a custom application;
• Added the option to save the sought keyword;
• Improved seeking settings saving;
• Improved Windows 8 and 8.1 support;
• Improved the user interface;
• Bug fixes.