The function_file function returns the path name of the file which defines the function name. If name is a built-in function, the string built-in is returned. If name is not a known function, function_file returns the null string.

If name is an ACL function not yet loaded but declared via autoload, function_file will return the null string by default. If the optional parameter load is specified and has a non-zero value, function_file will cause the function to be loaded to return the actual path name.