find . -name '*.php' -exec php -l {} \;

This is useful for just checking the basics. It will not show warnings or uninitialized variables.

Example output:

No syntax errors detected in ./application/helpers/dealertrend_plugin_updater.php
No syntax errors detected in ./application/helpers/dynamic_site_headers.php
No syntax errors detected in ./application/helpers/http_api_wrapper.php
No syntax errors detected in ./application/helpers/vehicle_management_system.php
No syntax errors detected in ./application/helpers/vehicle_reference_system.php
No syntax errors detected in ./application/views/inventory/armadillo/detail.php
No syntax errors detected in ./application/views/inventory/armadillo/index.php
No syntax errors detected in ./application/views/inventory/armadillo/list.php
No syntax errors detected in ./application/views/inventory/bobcat/detail.php
No syntax errors detected in ./application/views/inventory/bobcat/index.php
No syntax errors detected in ./application/views/inventory/bobcat/list.php
No syntax errors detected in ./application/views/mobile/websitez/detail.php
No syntax errors detected in ./application/views/mobile/websitez/index.php
No syntax errors detected in ./application/views/mobile/websitez/list.php
PHP Deprecated:  Call-time pass-by-reference has been deprecated in ./application/views/options/page.php on line 12
No syntax errors detected in ./application/views/options/page.php
No syntax errors detected in ./application/views/widgets/vehicle_management_system.php
No syntax errors detected in ./application/views/widgets/vehicle_reference_system.php
No syntax errors detected in ./dealertrend-inventory-api.php