Earlier this week I came across this PHP error on a Ubuntu server:
PHP Startup: Unable to load dynamic library '/usr/lib/php/20131226/curl.so' - /usr/lib/php/20131226/curl.so: undefined symbol: zend_unset_property in Unknown on line 0
After some research, I realised the best fix would be to update PHP CLI:
apt-get install php5.6-cli
This meant that I could now run composer without any issues.