Install Composer in MacOS Catalina

php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');"
php -r "if (hash_file('sha384', 'composer-setup.php') === '756890a4488ce9024fc62c56153228907f1545c228516cbf63f885e036d37e9a59d27d63f46af1d4d07ee0f76181c7d3') { echo 'Installer verified'; } else { echo 'Installer corrupt'; unlink('composer-setup.php'); } echo PHP_EOL;"
php composer-setup.php
php -r "unlink('composer-setup.php');"

Local or specific Directory: 

php composer-setup.php --install-dir=bin --filename=composer

Global: 

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

Note: If the above fails due to permissions, you may need to run it again with sudo.
Note: On some versions of macOS the /usr directory does not exist by default. If you receive the error "/usr/local/bin/composer: No such file or directory" then you must create the directory manually before proceeding: mkdir -p /usr/local/bin.

You can also follow instruction from: https://getcomposer.org/download/