#非www跳转到www的正则
$HTTP["host"] =~ "^([^.]*.[^.]*)$" {
  url.redirect = ( "^/(.*)" => "http://www.%1/$1" )
}

——正则表达式渣渣的个人备忘

如果你希望加一点特殊的域名允许他非www不跳转:

#非www跳转到www的正则
$HTTP["host"] =~ "^((?!hiwbb)[^.]*.[^.]*)$" {
  url.redirect = ( "^/(.*)" => "http://www.%1/$1" )
}

反过来操作?lighttpd内有示范:

##
## both rewrite/redirect support back reference to regex conditional using %n
## 
#$HTTP["host"] =~ "^www\.(.*)" {
#  url.redirect            = ( "^/(.*)" => "http://%1/$1" )
#}