In directory :
$ wc -l `find . -type f -name '*php'`
Result :
53 ./admin/admin-ajax.php
324 ./admin/index.php
84 ./admin/install.php
165 ./admin/plugins.php
(...)
69 ./yourls-loader.php
24862 total
Excluding directories :
$ wc -l `find . -type f -name '*php' | grep -v "includes/vendor"`