' in order to execute code.
Interactive shell evaluates every expression as you complete it (with ; or }), reports errors without terminating execution, and supports standard shell functionality via readline (history, tab completion, etc). It's an enhanced version of interactive mode that is ONLY available if you have the required libraries, and is an actual PHP shell that interprets everything you type as PHP code - using '<?php' will cause a parse error.
Finally, if you're running on Windows, you're probably screwed. From what I'm seeing in other comments here, you don't have readline, and without readline there is no interactive shell. 
 
10 
 spencer at aninternetpresence dot net ¶2 years ago
 In Windows, press Enter after your ending PHP tag and then hit Ctrl-Z to denote the end-of-file:
C:\>php -a
Interactive mode enabled
<?php
echo "Hello, world!";

$fp = fopen("php://stdin", "r");
$in = '';
while($in != "quit") {
    echo "php> ";
    $in=trim(fgets($fp));
    eval ($in);
    echo "\n";
    }
   

echo "Hello World!\r\n";
(Hit CTRL+D here)
Hello World!
This is NOT interactive mode, but may help you.
To have the "-i" available, you'll need the following arguments while compiling PHP:
--with-readline e --with-libedit 
 
0 
 Shane Harter ¶5 months ago
 If you've ever wanted to build your own interactive shell, I released a project recently that makes it insanely easy to build awesome shell apps in PHP. It blends features from Zend2 and Symonfy2 with things like regex routing, state management, etc. Check it out here: 
https://github.com/shaneharter/sheldon 
 
0 
 lee8oi at gmail dot com ¶1 year ago
 I use git-bash in windows to connect to my servers via SSH. When I use the interactive mode via 'php -a' command I have to hit ctrl+d twice to execute the entered code. Example:
(<ctrl+d> denotes hitting ctrl & D)
-bash$ php -a
Interactive mode enabled
<?php
echo 'hello world';

When building php on FreeBSD from ports one can add --with-readline option by manually editing the var CONFIGURE_ARGS in Makefile inside the php port directory and proceeding with build as usual.