macに homebrewをインストールする

/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"

phpの最新バージョンをインストールする

brew install php

既にhomebrewがインストールされておりhomebrewのversionが古く下記のエラーが発生した場合は、
homebrew自体のバージョンアップをして下さい。

brew update-reset

php インストール時のエラー

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
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!
Traceback (most recent call last):
	11: from /usr/local/Homebrew/Library/Homebrew/brew.rb:31:in `<main>'
	10: from /usr/local/Homebrew/Library/Homebrew/brew.rb:31:in `require_relative'
	 9: from /usr/local/Homebrew/Library/Homebrew/global.rb:79:in `<top (required)>'
	 8: from /usr/local/Homebrew/Library/Homebrew/vendor/portable-ruby/2.6.3_2/lib/ruby/2.6.0/rubygems/core_ext/kernel_require.rb:54:in `require'
	 7: from /usr/local/Homebrew/Library/Homebrew/vendor/portable-ruby/2.6.3_2/lib/ruby/2.6.0/rubygems/core_ext/kernel_require.rb:54:in `require'
	 6: from /usr/local/Homebrew/Library/Homebrew/os.rb:7:in `<top (required)>'
	 5: from /usr/local/Homebrew/Library/Homebrew/os.rb:43:in `<module:OS>'
	 4: from /usr/local/Homebrew/Library/Homebrew/os/mac.rb:65:in `prerelease?'
	 3: from /usr/local/Homebrew/Library/Homebrew/os/mac.rb:28:in `version'
	 2: from /usr/local/Homebrew/Library/Homebrew/os/mac/version.rb:32:in `from_symbol'
	 1: from /usr/local/Homebrew/Library/Homebrew/os/mac/version.rb:32:in `fetch'
/usr/local/Homebrew/Library/Homebrew/os/mac/version.rb:32:in `block in from_symbol': unknown or unsupported macOS version: :dunno (MacOSVersionError)

brew link してインストールしたPHPを使える様にする

brew link php

brew link php　で下記のエラーが発生した場合

Linking /usr/local/Cellar/php/8.1.1... 
Error: Could not symlink sbin/php-fpm
/usr/local/sbin is not writable.

(参考) brew link php71: Could not symlink sbin/php-fpm
https://stackoverflow.com/questions/46778133/brew-link-php71-could-not-symlink-sbin-php-fpm

I solved this problem by first creating the directory sbin:

sudo mkdir /usr/local/sbin

then if you are like me using macOS highSierra 10+ you need to run:

sudo chown -R $(whoami) $(brew --prefix)/sbin

after this

brew link php

動作確認

php -v

composerをinstallをする

Download Composer
https://getcomposer.org/download/

php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');"
php -r "if (hash_file('sha384', 'composer-setup.php') === '906a84df04cea2aa72f40b5f787e49f22d4c2f19492ac310e8cba5b96ac8b64115ac402c8cd292b8a03482574915d1a8') { echo 'Installer verified'; } else { echo 'Installer corrupt'; unlink('composer-setup.php'); } echo PHP_EOL;"
php composer-setup.php
php -r "unlink('composer-setup.php');"

sudo mv composer.phar /usr/local/bin/composer

動作確認

composer -v