suppose i redirect a domain home to a sub folder of same url does it hurt ranking in search engines ?
It might hurt your page for a little while, but Google should re-index it and take everything into consideration. That's assuming though your doing a 301 redirect.
It needs to be a permanent redirect. That is what Google advises webmasters. If you use Apache, there is an option for you or your web host has a panel where you can set it. The option is available in cpanel too.
Place one of the following in your htaccess file depending on if you are redirecting a page or entire site... For example, to redirect an entire web site to another site: Redirect 301 / http://www.mydomain.com/ Or, to redirect just one page to another page: Redirect 301 /old-page.html http://www.mydomain.com/new-page.html