puzzling php parser error

Ok maybe not so puzzling, but here it is.

I was messing around and noticed this, typing just <?php in a file, just that, no space after that, nothing else just the tag, throws a parse error.

With a single space it works fine. I was wondering if anyone knows why the parser chokes, since it is perfectly oka开发者_如何学Pythony otherwise to omit the closing tag. Thanks.

The PHP documentation says:

In PHP 5.2 and earlier, the parser does not allow the <?php opening tag to be the only thing in a file. This is allowed as of PHP 5.3.

With that said, in PHP 5.3, if you have short_open_tags set to On in your php.ini file, the error still shows up.

This answered in the PHP Documentation for Basic Syntax:

In PHP 5.2 and earlier, the parser does not allow the <?php opening tag to be the only thing in a file. This is allowed as of PHP 5.3.

However, by the OP it seems that the opening tag + space is allowed (i.e. not the only thing in a file). In addition, from the comments, it would seem that this is not the case for distro versions or otherwised patched.

My PHP version:

$ php -v
PHP 5.3.6 (cli) (built: Mar 17 2011 20:56:13) 
Copyright (c) 1997-2011 The PHP Group
Zend Engine v2.3.0, Copyright (c) 1998-2011 Zend Technologies
    with Xdebug v2.1.0, Copyright (c) 2002-2010, by Derick Rethans

The code in question:

$ echo -n "<?php" | php
<?php

Adding some more next to <?php:

$ echo -n "<?php/**/" | php
<?php/**/

or

$ echo -n "<?php;" | php
<?php;

and then a space:

$ echo -n "<?php " | php

(finally empty output).

That PHP version is not giving me a Parse error: syntax error, unexpected $end type of message for the examples above, but it does with this:

$ echo -n "<?php x" | php -d display_errors=1

Parse error: syntax error, unexpected $end in - on line 1

Hope it helps. In my eyes this looks like that the input is treated just as text until a whitespace follows up the <?php opening sequence.