Ruby on railsの環境構築エラー

Question

Ruby on railsの環境構築において、

brew install rbenv ruby-build

を実行したところ、以下のようなエラーが出て全く進められません。

どなたか原因と対策を教えてくださると嬉しいです。

==> Searching for similarly named formulae...
Error: No similarly named formulae found.
Error: No available formula or cask with the name "rbenv".
==> Searching for a previously deleted formula (in the last month)...
Error: No previously deleted formula found.
==> Searching taps on GitHub...
Error: No formulae found in taps.