$string is not showing in common.php - php

Question

Let's say I've got 2 files. 1 is common which loads all the design and stuff and one is index.
What I want to do is set a $ in index like this:
<?
$SubId3 = 'test';
include "../../common.php";
?>
Then in common I want to have something like
<?=$SubId3; if (empty($SubId3)) { echo 'homepage'; } ?>
I cannot seem to get this working. Meaning if I set it up this way. The index will never show "test".
What am i doing wrong here?
I want to do this since only certain files will contain the string $SubId3, to test some things on certain pages and not others (by adding $SubId3 = 'test'; to that particular file)

Answer 1

Note that <?= is short-hand to output something (think of <?= as <?php echo) and not to execute any other sort of logic or code.
However, it is possible to use the ternary operator this way:
<?= empty($SubId3) ? 'homepage' : $SubId3; ?>
This is basically equivalent to this:
<?php
if (empty($SubId3)) {
echo 'homepage';
}
else {
echo $SubId3;
}
?>
So the <?= short-hand should only be used to pass one simple variable or a ternary expression to it; everything else should use the common <?php tag.
Here's a test case for Alex (in the comments) because I can run the above code just fine with PHP 5.4.12, but he seems not to be able to.
common.php
<?= empty($SubId3) ? 'homepage' : $SubId3; ?>
index.php (visit this file then)
<?php
$SubId3 = 'test'; // <-- Comment this out for the "homepage" output
include 'common.php';

Answer 2

i think this
<?=$SubId3; if (empty($SubId3)) { echo 'homepage'; } ?>
should be
<?php $SubId3; if (empty($SubId3)) { echo 'homepage'; } ?>
<?=?> is short for <?php echo?>

Answer 3

This wont work:
<?=$SubId3; if (empty($SubId3)) { echo 'homepage'; } ?>
If you want to print some stuff, you have to use only the variable, in one block and the IF on another.
<?=$SubId3?>
And:
<?php if(empty($SubId3)) { echo 'homepage'; } ?>
Hope this helps...

Answer 4

Try
<?php
/* echo $SubId3; */
if (empty($SubId3)) {
echo 'homepage';
} else {
echo $SubId3;
}
?>
Consider using different style of coding.
In PHP you have generally three variants:
PHP code only
HTML files with just some echoes
Intermixed PHP and HTML
In first you use echo to output every single bit of the HTML.
Second means you include a PHP script at the top of your HTML file and call appropriate functions / insert text into the template. Just so you can edit your HTML separately from your PHP.
Third makes for sometimes unreadable and complex code, but is fast to write.
<?php if($something) {
while($otherthing) { ?>
<B>text=<?=$index ?></B>
<?php }} ?>
Just a food for thought.

Answer 5

I found the answer guys, thanks for all the help.
I needed to set it in the PrintHeader like this:
<?
include "../../common.php";
printHeader('BlogNr1', 'BlogNr2', 'BlogNr3');
?>
And the index had to look like this:
<?
include "../../common.php";
printHeader('BlogNr1', 'BlogNr2', 'BlogNr3');
?>
Somebody on skype helped me. thanks anyways guys!