Here's a simple one liner you can use to syntax check all php files in your working directory.

find . -type f -name "*.php" -exec php -l {} \; | grep -v 'No syntax errors'

For those not familiar with the programs used, it basically reads as.... Find all files that end in '.php' and with each of those files run php -l. This is then put through a pipe to the grep -v, which filters out all files that are syntactically correct.