TL;DR
In several occasions, I've solved this kind of errors by just closing my terminal session and opening a new one before retrying the failing command.
Long explanation
In some SOs (such as MacOS) there is already a pre-installed, system-wide version of ruby. If you are using a version manager, such as rbenv
or asdf
, they work by playing with the environment of your current session so that the relevant commands point to the binaries installed by the version manager.
When installing a new binary, the version manager installs it in a special location, usually somewhere under the user's home directory. It then configures everything in your PATH
so that you get the freshly installed binaries when you issue a command, instead of the ones that came with your system. However, if you don't restart the session (there are other ways of getting your environment updated, but that's the easiest one) you don't get the new configuration and you will be using the original installation.