how to install latest composer in mac

Open a terminal and navigate to your user directory, ie cd /User/<USER_NAME>/
Run this command shown below to download Composer. This will create a Phar (PHP Archive) file called
composer.phar:

curl -sS https://getcomposer.org/installer | php

Now we move 
composer.phar file to a directory
sudo mv composer.phar /usr/local/bin/

We want to run Composer with having to be root al the time, so we need to change the permissions:
sudo chmod 755 /usr/local/bin/composer.phar
 
Next, we need to let Bash know where to execute Composer: 
nano ~/.bash_profile

Add this line below to bash_profile and save
 
alias composer="php /usr/local/bin/composer.phar"
and then run this command:
 
source ~/.bash_profile
 
Finally, run: 
composer -v