Install OpCache on FreeBSD with (note 56 resembles the current PHP version 5.6):
cd /usr/ports/www/php56-opcache && sudo make config-recursive install distclean
Open up php.ini to configure OpCache settings:
sudo ee /usr/local/etc/php.ini
Check the OpCache running configuration in the command line with (note php -r 'var_dump(opcache_get_status());' can be used to check if OpCache is running, but results in CLI are unreliable):
php -r 'var_dump(opcache_get_configuration());'