Get variable names from an unknown Dataset

[Balinus]

I'm sure there is a way to the the variables names from a given Dataset but I haven't found a way or example yet. I have like
50 files, with 2 or 3 unknown variables name, and I would like to build a simple list out of the variable names. Thanks!

[lazarusA]

ds.cubes.keys

duplicated, see #487

[Balinus]

Thanks! I did use keys(ds) in my search for variable names!

Closing as it is a duplicate.