Reading $_POST in PHP / vB

[janaf]

New at php and vB:

I am using PHP direct-eval and using $_POST to read posted data but it seems it is not available with vB? I can not read the passed variable name / value:

PHP Code:

$output = $_POST["mystr"]; 


calling the page with

content.php?305&mystr=hi

Returns nothing

What are my options to pass / read data with vB / php?

I would like to have a simple pull-down menue and read it's value at post / submit, posting to the same page.

Is there another / better way to do this?

I also have a related post problem discribed here:
https://vborg.vbsupport.ru/showthread.php?t=248700

Any input appreciated...