this is my htaccess:

RewriteEngine On  
RewriteCond %{DOCUMENT_ROOT}%{REQUEST_URI} -f [OR]
RewriteCond %{DOCUMENT_ROOT}%{REQUEST_URI} -d
RewriteRule ^ - [L]

RewriteRule ^ /index.html [L]

RewriteEngine on
RewriteCond %{HTTP_HOST} ^shadyab.com [NC]
RewriteRule ^(.*)$ http://www.shadyab.com/$1 [L,R=301,NC]

but my site loaded with non www.

Set condition to any address not starting with www and then redirect.

RewriteCond %{HTTP_HOST} !^www\.
RewriteRule ^(.*)$ http://www.%{HTTP_HOST}/$1 [R=301,L]

Force www:

RewriteEngine on

RewriteCond %{HTTP_HOST} ^example.com [NC]

RewriteRule ^(.*)$ http://www.example.com/$1 [L,R=301,NC]

Force non-www:

RewriteEngine on

RewriteCond %{HTTP_HOST} ^www\.example\.com [NC]

RewriteRule ^(.*)$ http://example.com/$1 [L,R=301]