I'll just mention fsql[1] here as my favorite of the multiple programs available to query and manipulate different data formats. While more complex, as it requires SQL, that's also the reason I like it. In all the cases where I've had moderately sized lists of items and was tempted to stick them into a DB, fsql makes the job easier.

I want to check out rei though, as it looks like for some common tasks it could be much easier to use. It might make a good addition to my toolkit for the simpler cases.

1: https://metacpan.org/pod/distribution/App-fsql/bin/fsql

I like it, thanks for building it! So far I've used csvkit (https://csvkit.readthedocs.org/en/0.9.1/), which is quite powerful. Can `rei` also parse the header row of CSV files to automatically assign names to columns?

Just FYI, as your README.md starts with naming considerations, "rei" means king in portuguese. :)