upgrade composer version 2 code example

Example 1: upgrade composer version

composer self-update

Example 2: update composer php version

php7.3 -f /usr/local/bin/composer update

Example 3: composer upgrade to 2

run which composer (output /usr/bin/composer)
run php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');"
run sudo php composer-setup.php --install-dir=/usr/bin --filename=composer