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heavyhttpd, 2009-01-11 06:01
correct meaning of % substitutions

URL Rewrites

Module: mod_rewrite


internal redirects, url rewrite



Rewrites a set of URLs internally in the webserver BEFORE they are handled.


url.rewrite-once = ( "<regex>" => "<relative-uri>" )


Rewrites a set of URLs internally in the webserver BEFORE they are handled


url.rewrite-repeat = ( "<regex>" => "<relative-uri>" )

The difference between these options is that, while url.rewrite-repeat allows for applying multiple (seperately defined) rewrite rules in a row, url.rewrite-once will cause further rewrite rules to be skipped if the expression was matched. As such, url.rewrite-once behaves like Apaches' RewriteRule ... [L]:

The options url.rewrite and url.rewrite-final were mapped to url.rewrite-once in 1.3.16.

NOTE: url rewriting does not work within a $HTTP["url"] conditional. []

Regular Expressions

  • . (full stop) - match any character
  • \* (asterisk) - match zero or more of the previous symbol
  • \+ (plus) - match one or more of the previous symbol
  • ? (question) - match zero or one of the previous symbol
  • \\? (backslash-something) - match special characters
  • ^ (caret) - match the start of a string
  • $ (dollar) - match the end of a string
  • [set] - match any one of the symbols inside the square braces.
  • [^set] - match any symbol that is NOT inside the square braces.
  • (pattern) - grouping, remember what the pattern matched as a special variable
  • {n,m} - from n to m times matching the previous character (m could be omitted to mean >=n times)
  • (?!expression) - match anything BUT expression at the current position. Example: "^(/(?!(favicon.ico$|js/|images/)).*)" => "/fgci/$1"
  • Normal alphanumeric characters are treated as normal

Replacement Patterns

If the matched regex contains groups in parentheses, $1..$9 in the replacement refer to the captured text in the
matching group "$1" meaning the first group, "$2" the second, and so on.

Note that % replacements (like %1, %2, %0, etc.) in url.rewrite-* targets are permitted, but do not have the meaning they would have in evhost.path-pattern. If url.rewrite-* is specified within a regex conditional, % patterns are replaced by the corresponding groups from the condition regex. %1 is replaced with the first subexpression, %2 with the second, etc. %0 is replaced by the entire substring matching the regexp. See below for an example using "%0".


The regex is matching the full REQUEST_URI which is supplied by the user including


# the following example, is, however just simulating vhost by rewrite
# * you can never change document-root by mod_rewrite
# use mod_*host instead to make real mass-vhost

server.document-root = "/www/htdocs/" 
$HTTP["host"] =~ "^.*\.([^.]+\.com)$" {
  url.rewrite-once = ( "^/(.*)" => "/%0/$1" )

# request: 
# before rewrite: REQUEST_URI="/www/htdocs/url/" 
# and DOCUMENT_ROOT="/www/htdocs/" %0="" $1="url/" 
# after rewrite:  REQUEST_URI="/www/htdocs/" 
# still, you have DOCUMENT_ROOT=/www/htdocs/

# please note, that we have two regular expressions: the one which 
# $HTTP["host"] is been compared with, and the one of the rewrite rule.
# the numbered subexpressions available to build the relative uri are
# being prefixed by '%' for subexpressions of the first regular expression 
# match and by '$' for subexpressions of the second one.
# subexpression 0 interpolates the whole matching string: %0 for the whole
# string matching the conditional, and $0 for the whole string matching the
# rewrite rule.

# if the rewrite rule is not included in a conditional 
# block, only the '$' prefixed variables are available.

url.rewrite-once = ( "^/id/([0-9]+)$" => "/index.php?id=$1",
                     "^/link/([a-zA-Z]+)" => "/index.php?link=$1" )

With mod_redirect

Rewrite rules always execute before redirect rules. This is true regardless of the order of module loading or the order of rules in the configuration (lighttpd v1.4.13). However, mod_rewrite provides a mechanism to pass URLs through unmangled: specify "$0" as the rule target.


url.rewrite-once = (
    "^/foo"  => "$0",
    "^/(.*)" => "/handler/$1" 

url.redirect = (
    "^/foo"  => "" 

Workaround for "File name too long" on Windows

While running Lighttpd on Windows you may get 500 Internal Server Error if computed filename is longer than 255 symbols.
In error log it will be (response.c.537) file not found ... or so: File name too long /very_looooong_path ->.
As workaround you can use mod_rewrite to avoid this error.

server.modules += ("mod_rewrite")
url.rewrite-once = ( ".{250,}" => "/toolong.php" )

If error handler is PHP, $_SERVER['REQUEST_URI'] will contain full URI.

Passing / Matching the Query string (GET variables)

If you wanna pass the Query String (?foo=bar) to the rewrite destination you have to explicitly match it:

url.rewrite-once = (
    "^/news/([^\?]+)(\?(.*))?" => "/news.php?title=$1&$3" 

Updated by heavyhttpd over 11 years ago · 45 revisions