Include and require are both used to insert the content of one PHP file into another PHP file. These two functions are identical. What makes the difference is the way they handle errors.

If an error occurs, the include() function generates a warning, but the script will continue execution. The require() generates a fatal error, and the script will stop. That is why it is recommended to use the require() function instead of include().

Not all of PHP installation has short tags support. There are a few installations that have turned it off. If the short tags are turned off, only <?php and <script> tags are recognized. The <? tags are not allowed and the scripts are broken.

If you want to use the PHP short tag <? you need to edit the php.ini file and set short_open_tag to on:

short_open_tag = On

Using short tags should be avoided when developing applications that are meant for redistribution, or deployment on PHP servers which are not under your control, because short tags may not be supported on the target server. Besides short tags are considered bad because they are in conflict with XML’s open tag ‘<?xml’.

For portable reason, redistributable code, be sure not to use short tags.