Wow this is a gem of a comment. I use Recoll heavily, it's a real super power for an academic, but I had no idea about rclgrep. Thank you for all your work.
What rclgrep does is run the recoll text extraction and do a grep-like operation on the extracted texts. If you want to give it a try, don't hesitate to contact me if you have any trouble building or using it, or think it could be improved. It's more or less a (working) prototype at the moment, but I'm willing to expand it if it looks useful. The "Usage" string is much better in the latest git source than in the tar, and it sorely needs a man page.