These are the steps to install composer on MAC OS X to work with MAMP php

composer_mamp_osx.sh

# Global composer install for MAMP Users on OSX
# http://getcomposer.org/doc/00-intro.md#globally
# For PHP 5.4 Use:
# alias php=/Applications/MAMP/bin/php/php5.4.4/bin/php; 
 
alias php=/Applications/MAMP/bin/php/php5.3.6/bin/php; 
curl -sS https://getcomposer.org/installer | php;
mv composer.phar /usr/local/bin/composer;
composer help;