RewriteEngine

○wwwありに統一
RewriteEngine on
RewriteCond %{HTTP_HOST} ^example\.com
RewriteRule (.*) http://www.example.com/$1 [R=301,L]

○wwwなしに統一
RewriteEngine on
RewriteCond %{HTTP_HOST} ^www\.example\.com
RewriteRule (.*) http://example.com/$1 [R=301,L]