Remember a function that can directly output the PHP source code? What should I do?

Remember a function that can directly output the PHP source code ?? I used a function to directly output the PHP source code to the page instead of the result after executing the PHP code? What is a function... How can I read php files? Fopen? File? Curl? File_get_contents and so on do not seem to work. ...... remember a function that can directly output PHP source code ??
I used a function to directly output the PHP source code to the page instead of the result after executing the PHP code? What is a function...
How can I read php files? Fopen? File? Curl? None of file_get_contents seem to work .....

------ Solution --------------------
Echo file_get_contents ("test. php ");
?>