Error: No formulae or casks found for "php8".

brew search php8

↑コマンドにてインストールできるphp8系を探そうとしたところ、掲題のエラーが、、

homebrewのバージョンが古いのかと思いupdateを試みる。。

brew update

が、しかし、また怒られる。。

Error: 
  homebrew-core is a shallow clone.
  homebrew-cask is a shallow clone.
To `brew update`, first run:
  git -C /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core fetch --unshallow
  git -C /usr/local/Homebrew/Library/Taps/homebrew/homebrew-cask fetch --unshallow
These commands may take a few minutes to run due to the large size of the repositories.
This restriction has been made on GitHub's request because updating shallow
clones is an extremely expensive operation due to the tree layout and traffic of
Homebrew/homebrew-core and Homebrew/homebrew-cask. We don't do this for you
automatically to avoid repeatedly performing an expensive unshallow operation in
CI systems (which should instead be fixed to not use shallow clones). Sorry for
the inconvenience!

このコマンドを実行しなさいと神のお告げ。言われるままに↓を実行

git -C /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core fetch --unshallow
git -C /usr/local/Homebrew/Library/Taps/homebrew/homebrew-cask fetch --unshallow

再度updateを試みる

brew update

すると、、

Already up-to-date.

やったー！！！大成功！！！

ほっと一息。

再度インストールできるphp8系を探すと

brew search php8

==> Formulae
php@8.0 ✔

はい、でたー！！！

そしてインストール

brew install php@8.0

これで無事インストール完了。