I'm utilizing a contact page wordpress plugin for my blog.The shortcode using with this is [my-shortcode]. Can there be anyways to filter just the shortcode in the content. Eg: Test post [my-shortcode] Demo widget.here i have to filter just the shortcode.Thanks

You should use regex to obtain the worth of brackets inside a string like so.

if(preg_match_all('/\[(.*?)\]/',$_POST['my_key'],$matches))
{
    foreach($matches as $match)
    {
        if($match[1] == 'my-short-code')
        {
            //Do whetever
            break 2;
        }
    }
}

Note: match[1] might be match[0]