How do I remove keys?

This is not a feature right now to be able to do in one shot (see the comments in the DEL documentation). Unfortunately, you are only left with using KEYS, looping through the results, and then using DEL to remove each one.

How about using bash a bit to help?

for key in `echo 'KEYS user*' | redis-cli | awk '{print $1}'`
 do echo DEL $key
done | redis-cli

To step through it:

1. echo 'KEYS user*' | redis-cli | awk '{print $1}' -- get all the keys and strip out the extra text you don't want with awk.
2. echo DEL $key -- for each one, create an echo statement to remove it.
3. | redis-cli -- take the DEL statements and pass them back into the cli.

Not suggesting this is the best approach (you might have some issues if some of your usernames have spaces in them, but hopefully you get the point).

Another compact one-liner I use to do what you want is:

redis-cli KEYS "user*" | xargs redis-cli DEL