What's a standalone open source project that does file searching?

I have a php webpage with a search bar that uses php code to search my server for files. It's really slow. It's a custom made thing I came up with years ago.

Are there any standalone python or c++ projects or libraries I can use that handle file searching? Plugging in a more optimal search function into this system would be a massive improvement but I can't really replace this with a different system because reasons. If the only way to get such a feature is if I program it myself, then I'll have to do that as it will be less work than migrating to a new system. But I'm pretty sure there exists something I could use to manage the search so I can shoehorn that in to the codebase instead of starting from scratch. Any suggestions?

Tl;dr I'm looking for a command line search program that runs on Linux and has some form of indexing.