Global Installation of Composer (manual)

As described on the Composer website:

curl -sS https://getcomposer.org/installer | php
sudo mv composer.phar /usr/local/bin/composer

Manual Method

you can run easier way to globally install composer than the manual proscribed in the github readme.md. It's actually on the getcomposer.org website:

curl -s http://getcomposer.org/installer | php
sudo mv composer.phar /usr/local/bin/

And you can try this way also, create an alias:

alias composer='/usr/local/bin/composer.phar'

Read More: https://realprogrammer.in/global-installation-of-composer-manual/