Apache HTTP Server Version 2.4
Historically, there are several syntax variants for expressions used to express a condition in the different modules of the Apache HTTP Server. There is some ongoing effort to only use a single variant, called ap_expr, for all configuration directives. This document describes the ap_expr expression parser.
The ap_expr expression is intended to replace most other
expression variants in HTTPD. For example, the deprecated
SSLRequire
expressions can be
replaced by Require expr.
<If>
<ElseIf>
<Else>
AuthBasicFake
AuthFormLoginRequiredLocation
AuthFormLoginSuccessLocation
AuthFormLogoutLocation
RewriteCond
SetEnvIfExpr
Header
RequestHeader
FilterProvider
Require ldap-user
Require ldap-group
Require ldap-dn
Require ldap-attribute
Require ldap-filter
SSLRequire
LogMessage
mod_include
Backus-Naur Form (BNF) is a notation
technique for context-free grammars, often used to describe the syntax of languages used in computing.
In most cases, expressions are used to express boolean values.
For these, the starting point in the BNF is expr
. However, a few directives
like LogMessage
accept expressions
that evaluate to a string value. For those, the starting point in the BNF is string
.
expr ::= "true" | "false" | "!" expr | expr "&&" expr | expr "||" expr | "(" expr ")" | comp comp ::= stringcomp | integercomp | unaryop word | word binaryop word | word "in" "{" wordlist "}" | word "in" listfunction | word "=~" regex | word "!~" regex stringcomp ::= word "==" word | word "!=" word | word "<" word | word "<=" word | word ">" word | word ">=" word integercomp ::= word "-eq" word | word "eq" word | word "-ne" word | word "ne" word | word "-lt" word | word "lt" word | word "-le" word | word "le" word | word "-gt" word | word "gt" word | word "-ge" word | word "ge" word wordlist ::= word | wordlist "," word word ::= word "." word | digit | "'" string "'" | """ string """ | variable | rebackref | function string ::= stringpart | string stringpart stringpart ::= cstring | variable | rebackref cstring ::= ... digit ::= [0-9]+ variable ::= "%{" varname "}" | "%{" funcname ":" funcargs "}" rebackref ::= "$" [0-9] function ::= funcname "(" word ")" listfunction ::= listfuncname "(" word ")"
The expression parser provides a number of variables of the form
%{HTTP_HOST}
. Note that the value of a variable may depend
on the phase of the request processing in which it is evaluated. For
example, an expression used in an <If >
directive is evaluated before authentication is done. Therefore,
%{REMOTE_USER}
will not be set in this case.
The following variables provide the values of the named HTTP request
headers. The values of other headers can be obtained with the
req
function. Using these
variables may cause the header name to be added to the Vary
header of the HTTP response, except where otherwise noted for the
directive accepting the expression. The req_novary
function may be used to circumvent this
behavior.
Name |
---|
HTTP_ACCEPT |
HTTP_FORWARDED |
HTTP_HOST |
HTTP_PROXY_CONNECTION |
HTTP_REFERER |
HTTP_USER_AGENT |
Other request related variables
Name | Description |
---|---|
REQUEST_METHOD |
The HTTP method of the incoming request (e.g.
GET ) |
REQUEST_SCHEME |
The scheme part of the request's URI |
REQUEST_URI |
The path part of the request's URI |
DOCUMENT_URI |
Same as REQUEST_URI |
REQUEST_FILENAME |
The full local filesystem path to the file or script matching the
request, if this has already been determined by the server at the
time REQUEST_FILENAME is referenced. Otherwise, such
as when used in virtual host context, the same value as
REQUEST_URI |
SCRIPT_FILENAME |
Same as REQUEST_FILENAME |
LAST_MODIFIED |
The date and time of last modification of the file in the format
20101231235959 , if this has already been determined by
the server at the time LAST_MODIFIED is referenced.
|
SCRIPT_USER |
The user name of the owner of the script. |
SCRIPT_GROUP |
The group name of the group of the script. |
PATH_INFO |
The trailing path name information, see
AcceptPathInfo |
QUERY_STRING |
The query string of the current request |
IS_SUBREQ |
"true " if the current request is a subrequest,
"false " otherwise |
THE_REQUEST |
The complete request line (e.g.,
"GET /index.html HTTP/1.1 ") |
REMOTE_ADDR |
The IP address of the remote host |
REMOTE_HOST |
The host name of the remote host |
REMOTE_USER |
The name of the authenticated user (if any) |
REMOTE_IDENT |
The user name set by mod_ident |
SERVER_NAME |
The ServerName of
the current vhost |
SERVER_PORT |
The server port of the current vhost, see
ServerName |
SERVER_ADMIN |
The ServerAdmin of
the current vhost |
SERVER_PROTOCOL |
The protocol used by the request |
DOCUMENT_ROOT |
The DocumentRoot of
the current vhost |
AUTH_TYPE |
The configured AuthType
(e.g. "basic ") |
CONTENT_TYPE |
The content type of the response |
HANDLER |
The name of the handler creating the response |
HTTPS |
"on " if the request uses https,
"off " otherwise |
IPV6 |
"on " if the connection uses IPv6,
"off " otherwise |
REQUEST_STATUS |
The HTTP error status of the request |
REQUEST_LOG_ID |
The error log id of the request (see
ErrorLogFormat ) |
CONN_LOG_ID |
The error log id of the connection (see
ErrorLogFormat ) |
CONN_REMOTE_ADDR |
The peer IP address of the connection (see the
mod_remoteip module) |
Misc variables
Name | Description |
---|---|
TIME_YEAR |
The current year (e.g. 2010 ) |
TIME_MON |
The current month (1 , ..., 12 ) |
TIME_DAY |
The current day of the month |
TIME_HOUR |
The hour part of the current time
(0 , ..., 23 ) |
TIME_MIN |
The minute part of the current time |
TIME_SEC |
The second part of the current time |
TIME_WDAY |
The day of the week (starting with 0
for Sunday) |
TIME |
The date and time in the format 20101231235959 |
SERVER_SOFTWARE |
The server version string |
API_VERSION |
The date of the API version (module magic number) |
Some modules register additional variables, see e.g. mod_ssl
.
With the exception of some built-in comparison operators, binary
operators have the form "-[a-zA-Z][a-zA-Z0-9_]+
", i.e. a
minus and at least two characters. The name is not case sensitive.
Modules may register additional binary operators.
Name | Alternative | Description |
---|---|---|
== |
= |
String equality |
!= |
String inequality | |
< |
String less than | |
<= |
String less than or equal | |
> |
String greater than | |
>= |
String greater than or equal | |
-eq |
eq |
Integer equality |
-ne |
ne |
Integer inequality |
-lt |
lt |
Integer less than |
-le |
le |
Integer less than or equal |
-gt |
gt |
Integer greater than |
-ge |
ge |
Integer greater than or equal |
Name | Description |
---|---|
-ipmatch |
IP address matches address/netmask |
-strmatch |
left string matches pattern given by right string (containing wildcards *, ?, []) |
-strcmatch |
same as -strmatch , but case insensitive |
-fnmatch |
same as -strmatch , but slashes are not matched by
wildcards |
Unary operators take one argument and have the form
"-[a-zA-Z]
", i.e. a minus and one character.
The name is case sensitive.
Modules may register additional unary operators.
Name | Description | Restricted |
---|---|---|
-d |
The argument is treated as a filename. True if the file exists and is a directory | yes |
-e |
The argument is treated as a filename. True if the file (or dir or special) exists | yes |
-f |
The argument is treated as a filename. True if the file exists and is regular file | yes |
-s |
The argument is treated as a filename. True if the file exists and is not empty | yes |
-L |
The argument is treated as a filename. True if the file exists and is symlink | yes |
-h |
The argument is treated as a filename.
True if the file exists and is symlink
(same as -L ) | yes |
-F |
True if string is a valid file, accessible via all the server's currently-configured access controls for that path. This uses an internal subrequest to do the check, so use it with care - it can impact your server's performance! | |
-U |
True if string is a valid URL, accessible via all the server's currently-configured access controls for that path. This uses an internal subrequest to do the check, so use it with care - it can impact your server's performance! | |
-A |
Alias for -U | |
-n |
True if string is not empty | |
-z |
True if string is empty | |
-T |
False if string is empty, "0 ", "off ",
"false ", or "no " (case insensitive).
True otherwise. | |
-R |
Same as "%{REMOTE_ADDR} -ipmatch ... ", but more efficient
|
The operators marked as "restricted" are not available in some modules
like mod_include
.
Normal string-valued functions take one string as argument and return a string. Functions names are not case sensitive. Modules may register additional functions.
Name | Description | Restricted |
---|---|---|
req , http |
Get HTTP request header; header names may be added to the Vary header, see below | |
req_novary |
Same as req , but header names will not be added to the
Vary header | |
resp |
Get HTTP response header | |
reqenv |
Lookup request environment variable (as a shortcut, v can be used too to access variables). | |
osenv |
Lookup operating system environment variable | |
note |
Lookup request note | |
env |
Return first match of note , reqenv ,
osenv | |
tolower |
Convert string to lower case | |
toupper |
Convert string to upper case | |
escape |
Escape special characters in %hex encoding | |
unescape |
Unescape %hex encoded string, leaving encoded slashes alone; return empty string if %00 is found | |
base64 |
Encode the string using base64 encoding | |
unbase64 |
Decode base64 encoded string, return truncated string if 0x00 is found | |
md5 |
Hash the string using MD5, then encode the hash with hexadecimal encoding | |
sha1 |
Hash the string using SHA1, then encode the hash with hexadecimal encoding | |
file |
Read contents from a file | yes |
filesize |
Return size of a file (or 0 if file does not exist or is not regular file) | yes |
The functions marked as "restricted" are not available in some modules
like mod_include
.
When the functions req
or http
are used,
the header name will automatically be added to the Vary header of the
HTTP response, except where otherwise noted for the directive accepting
the expression. The req_novary
function can be used to
prevent names from being added to the Vary header.
In addition to string-valued functions, there are also list-valued functions which
take one string as argument and return a wordlist, i.e. a list of strings. The wordlist
can be used with the special -in
operator.
Functions names are not case sensitive.
Modules may register additional functions.
There are no built-in list-valued functions. mod_ssl
provides PeerExtList
. See the description of
SSLRequire
for details
(but PeerExtList
is also usable outside
of SSLRequire
).
The following examples show how expressions might be used to evaluate requests:
# Compare the host name to example.com and redirect to www.example.com if it matches <If "%{HTTP_HOST} == 'example.com'"> Redirect permanent / http://www.example.com/ </If> # Force text/plain if requesting a file with the query string contains 'forcetext' <If "%{QUERY_STRING} =~ /forcetext/"> ForceType text/plain </If> # Only allow access to this content during business hours <Directory "/foo/bar/business"> Require expr "%{TIME_HOUR} -gt 9 && %{TIME_HOUR} -lt 17" </Directory>
Name | Alternative | Description |
---|---|---|
-in |
in |
string contained in string list |
/regexp/ |
m#regexp# |
Regular expression (the second form allows different delimiters than /) |
/regexp/i |
m#regexp#i |
Case insensitive regular expression |
$0 ... $9 |
Regular expression backreferences |
The strings $0
... $9
allow to reference
the capture groups from a previously executed, successfully
matching regular expressions. They can normally only be used in the
same expression as the matching regex, but some modules allow special
uses.
The ap_expr syntax is mostly a superset of the syntax of the
deprecated SSLRequire
directive.
The differences are described in SSLRequire
's documentation.
The req_novary
function
is available for versions 2.4.4 and later.