Install composer on docker

Dockerfile

FROM php:7.3-cli

###
# install homepage
RUN php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');" \
    && php -r "if (hash_file('sha384', 'composer-setup.php') === 'a5c698ffe4b8e849a443b120cd5ba38043260d5c4023dbf93e1558871f1f07f58274fc6f4c93bcfd858c6bd0775cd8d1') { echo 'Installer verified'; } else { echo 'Installer corrupt'; unlink('composer-setup.php'); } echo PHP_EOL;" \
    && php composer-setup.php --install-dir=/usr/local/bin --filename=composer \
    && php -r "unlink('composer-setup.php');"

###
# shell
RUN curl -sS https://getcomposer.org/installer | php -- --install-dir=/usr/local/bin/ --filename=composer 

###
# composer multi builder
FROM composer:1 AS composer

COPY --from=composer /usr/bin/composer /usr/bin/composer