Can meta tag description be declared dynamically in a web page - seo

Question

I have a dynamic page, where the contents and title will change based on the parameters in the URL. I want the same to be done for meta tag description. As I don't have a sound knowledge of SEO, I don't know whether it will be valid or not.
Say suppose URL contains word "test"
I will do,
if("test" is present)
{
<title>test</test>
<meta decription="test"/>
}
else
{
<title>test1</test>
<meta decription="test1"/>
}
Can I do this? Does giving two meta tag descriptions for same page work.

Answer 1

It is best practice to have different, on the page content based values of the title element and the meta description for each web page. It is not forbidden by the the HTML5 specification to have multiple <meta name="description" content="YOUR DESCRIPTION"> elements but I would guess that search engines process only the first appearance of the element. So my recommendation would be use one <meta name="description" content="YOUR DESCRIPTION"> element for each page.

Answer 2

As long as you code it server-side (eg in PHP) when the page is generated rather than client-side (javascript) after the page has loaded, then it will be fine. That's how most CMS systems work already.
Done server-side, only one of the description tags will actually appear in the code Google see.
Done client-side, it is likely that they will see no description at all as I don't think many search engines render javascript.