If you're looking for an open-source text search program for your Android device, aGrep by Aquamarine Networks is a great option. With aGrep, you can easily search for text in files located on your SD card. The program supports regular expressions and can be initiated with a SEARCH-intent. The search results are displayed with the filename, line number, and content.

One of the best features of aGrep is its internal text viewer, which allows you to view the searched text without having to open another application. Additionally, the program is equipped with an auto-detect multi char-code feature, which makes it easy to search for text in files with different character encoding.

It's important to note that aGrep is not designed for searching in system directories. If you encounter any issues or have any feedback, you can contact the developer by email or Twitter handle