初学者的好奇心

Question

I have a following question. I have put a long text (variable type LONGTEXT) into MYSQL database - through command line. Somewhere in this text there's a <br> tag, and near the end of text there's <?php phpinfo(); ?>. If i type SELECT * FROM mytable WHERE id=1, this whole text shows as it is, so it is unaltered (read: both <br> AND <?php phpinfo(); ?> are there. But when I submit query via php like this:

if (mysql_num_rows($result) > 0) {
  while($row = mysql_fetch_row($result)) {
    echo $row[1];
  }
}

Then the text is displayed exactly as I want it on my webpage, that means that <br> tag is processed by the browser as newline, AND <?php phpinfo(); ?> part is IGNORED. That is actually exactly what I want. But my question IS: WHY doesn't <?php phpinfo(); ?> part get processed via browser?? Does the PHP's echo function ignore the <?php tag??

Thanks in advance for explanations.

Answer 1

Because echoing a string is not the same as evaluating it.

PHP generates HTML, which is then processed by the browser. However a string containing PHP code won't be evaluated unless you specifically put it through eval() (hint: DON'T!)