Why doesn't PHP's Autoload feature work in CLI mode?

Question

This is more for my own personal edification than anything else but, this is something that has always bothered me: Why specifically can't PHP perform "autoloading" while in CLI mode?

I've been reading this disclaimer for years, but I've never read anything that touches on why:

http://php.net/manual/en/language.oop5.autoload.php:

Note: Autoloading is not available if using PHP in CLI interactive mode.

Does anyone know what is preventing PHP, as a language, from autoloading while working in CLI mode?

Answer 1

The way to think about PHP's interactive CLI is basically: PHP starting an empty script, and reading a file from PHP://stdin, which it then parses and executes. The file location, and therefore include path, and other environment variables are ignored. The current __FILE__, if you will does not exist.
Well, that's just a way of looking at it, it doesn't tell the whole story (far from it), but in practice, that's the way you can think of it. There needn't be a file to start in interactive CLI, at all:

$ php '<?php echo "this is read from STDIN"; ?>'

As can be deduced from the docs:

args...                    Arguments passed to script. Use -- args when first argument                               starts with - or script is read from stdin

Answer 2

Autoloading on the command line works. Do note the mention of "interactive".

PHP comes with two interactive modes, but unfortunately both of them are invoked by using php -a on your command shell.

If PHP is compiled with readline support, you get the "interactive shell". In this mode, every command is evaluated nearly instantly, and you also get instant feedback about any parsing errors.

In this mode, autoloading works.

The other mode is called "interactive mode". This mode is void of any fancy stuff, it only emits a short message, and then you basically write a PHP script - and nothing gets done unless you close the STDIN. Only then the written code gets parsed and executed. And this is the only case where the __autoload() function is not called for unknown classes.

Example for an interactive shell session (using PHP 5.3.2 on Linux):

vagrant@lucid32:/etc/apache2$ php -a
Interactive shell

php > function __autoload($classname) {
php { echo "Autoload $classname";
php { eval("class $classname{}");
php { return true;
php { }
php > new Bar();
Autoload ▒▒Bar
php > new FooBar();
Autoload ▒▒FooBar
php > var_dump($a = get_declared_classes());
array(123) {
[0]=>
string(8) "stdClass"
[1]=>
string(9) "Exception"
[2]=>
string(14) "ErrorException"
   ... lots of internal classes here ...
[121]=>
string(3) "Bar"
[122]=>
string(6) "FooBar"
}
php >

Example for an interactive mode (using PHP 5.3.18 on Windows)

PS C:\Users\sven> php -a
Interactive mode enabled

<?php
function __autoload($class) { echo "Auto: $class"; eval("class $class {}"); }
echo "Hello World";
$x = new Foo;
var_dump($x);
var_dump($a = get_declared_classes());
^Z
Hello World
Fatal error: Class 'Foo' not found in - on line 4

Call Stack:
  100.6337    1114608   1. {main}() -:0