Apache Rewritecond Rules Parameter Introduction

Summary:The Rewritecond directive defines the conditions under which a rule is valid, that is, one or more rewritecond directives can be preceded by a rewriterule instruction. The rewrite rule after the condition will only work if the current URI matches the pattern and satisfies the conditions here.

The Apache module Mod_rewrite provides a rewrite engine based on the regular expression parser to rewrite URL requests in real time. It supports a flexible and powerful URL manipulation mechanism in which each full rule can have an unlimited number of sub-rules and additional conditional rules. This URL operation can depend on a variety of tests, such as server variables, environment variables, HTTP headers, time stamps, and even lookup databases that match the URL component in various formats.

This module can manipulate all parts of the URL, including the path Information section, both at the server level (httpd.conf) and at the directory-level (. htaccess) configuration, and can also generate a final request string. The result of this override operation can be internal sub-processing, or it can be a steering of an external request, or even an internal agent processing.

Here is an introduction to the rules of Rewritecond and parameter descriptions. The Rewritecond directive defines the conditions under which a rule is valid, that is, one or more rewritecond directives can be preceded by a rewriterule instruction. The rewrite rule after the condition will only work if the current URI matches the pattern and satisfies the conditions here (TestString can match the Condpattern).

"description" defines the condition that overrides occur
"Grammar" Rewritecond teststring Condpattern [flags]
Scope Server config, virtual host, directory,. htaccess
"Overlay" FileInfo
"State" extension (E)
"Module" Mod_rewrite

TestString is a plain-text string, but it can also contain the following extensible components:
1, Rewriterule reverse reference, the reference method is: $N (0 <= N <=9) refers to the current (with a number of rewriterule instructions) Rewritecond in the pattern matching the grouping component (parentheses!).
2, Rewritecond reverse reference, the reference method is:%N (1 <= N <=9) refers to the current several rewritecond conditions in the last qualifying conditions of the grouping component (parentheses!).
3, Rewritemap extension, the reference method is: ${mapname:key|default} details see the rewritemap directive.
4, the server variable, the reference method is:%{name_of_variable}name_of_variable can be one of the strings listed in the following table:

HTTP Header	Connection and request
Http_user_agent Http_referer Http_cookie http_forwarded Http_host Http_proxy_connection Http_accept	Remote_addr Remote_host Remote_port Remote_user Remote_ident Request_method Script_filename Path_info Query_string Auth_type
Server itself	Date and Time	other
Document_root Server_admin server_name Server_addr Server_port Server_protocol Server_software	Time_year Time_mon Time_day Time_hour Time_min Time_sec Time_wday Time	Api_version The_request Request_uri Request_filename Is_subreq HTTPS

These variables correspond to similar named HTTP MIME headers, c variables of the Apache server, Structtm fields in Unix systems, most of which are described in other manuals or CGI specifications. The variables that are unique to mod_rewrite are as follows:

Is_subreq
If the request being processed is a child request, it will contain the string "true", otherwise it is "false". The module may produce a child request in order to parse the attached file in the URI.
Api_version
This is the version of the Apache module API that is in use (internal interface between the server and the module), which is defined in Include/ap_mmn.h. This module API version corresponds to the version of Apache being used (for example, this value is 19,990,320:10 in the release version of Apache1.3.14). In general, it is the developer of the module that is interested in it.
The_request
This is the full HTTP request line sent by the browser (for example: "get/index.htmlhttp/1.1"). It does not contain any other header information sent by the browser.
Request_uri
This is the resource requested in the HTTP request line (for example, "/index.html" in the above example).
Request_filename
This is the file path name of the complete local file system that matches the request.
HTTPS
If the connection uses SSL/TLS, it will contain the string "on" or "Off" (the variable can be used safely regardless of whether the mod_ssl has been loaded).

Other considerations:
1, Script_filename and request_filename contain the same values-that is, the filename field in the REQUEST_REC structure inside the Apache server. The first is the CGI variable name that everyone knows, and the second is a copy of Request_uri (the URI field in the REQUEST_REC structure).
2, special form:%{env:variable}, where the variable can be any environment variable. It is obtained by searching the Apache internal structure or (if not found) by the Apache server process through getenv ().
3, special form:%{ssl:variable}, where the variable can be the name of an SSL environment variable, regardless of whether the Mod_ssl module has been loaded can be used (not loaded when the empty string). For example:%{ssl:ssl_cipher_usekeysize} will be replaced with 128.
4, special form:%{http:header}, where the header can be the name of any httpmime header. It can always be obtained by looking up HTTP requests. For example:%{http:proxy-connection} will be replaced with the value of the proxy-connection:http header.
5, default form:%{la-u:variable}, the final value of variable is determined after an internal (URL-based) child request is executed. Use this method when you need to use a variable that is currently unknown but will be set in the subsequent procedure. For example, you need to use%{la-u:remote_user} in order to override the Remote_user variable in a server-level configuration (httpd.conf file). Because this variable is set by the authentication step after the URL rewrite (mod_rewrite) step. On the other hand, because Mod_rewrite is configured with the API remediation steps for the directory-level (. htaccess file), the authentication step is preceded by the API remediation step, so you can use%{remote_user}.
6, default form:%{la-f:variable}, the final value of the variable is determined after an internal (file-based) child request is executed. In most cases, the la-u is the same as above.

Condpattern is a conditional pattern, which is a regular expression applied to the current teststring instance. TestString will be calculated first and then matched with Condpattern.

Note: Condpattern is a Perl-compatible regular expression, but there are several additions:
1, can be used at the beginning of the Condpattern string '! ' (exclamation point) to specify a mismatch.
2, Condpatterns has a number of special variants. In addition to the standard usage of regular expressions, there are the following uses:

' <condpattern ' (less than the dictionary order)
Treats Condpattern as a pure string, compared to teststring by dictionary order. True if TestString is less than Condpattern.
' >condpattern ' (dictionary order greater than)
Treats Condpattern as a pure string, compared to teststring by dictionary order. True if TestString is greater than condpattern.
' =condpattern ' (dictionary order equals)
Treats Condpattern as a pure string, compared to teststring by dictionary order. True if TestString equals Condpattern (two strings are exactly equal by character). If Condpattern is "" (two double quotes), then teststring will be compared to an empty string.
'-d ' (directory)
Treat TestString as a pathname and test whether it is a directory that exists.
'-f ' (regular file)
Treat teststring as a path name and test whether it is a regular file that exists.
'-S ' (non-empty regular file)
Treat TestString as a pathname and test whether it is an existing regular file with a size greater than 0.
'-l ' (symbolic Connection)
Treat TestString as a pathname and test whether it is an existing symbolic connection.
'-X ' (executable)
Treat TestString as a pathname and test whether it is an existing file with executable permissions. This permission is detected by the operating system.
'-f ' (Files that exist on a child request)
Check if teststring is a valid file and can be accessed under the current access control configuration of the server. It uses an internal sub-request to do the check, because it will reduce the performance of the server, so please use it carefully!
'-u ' (the URL that exists for a child request)
Check if teststring is a valid URL and can be accessed under the current access control configuration of the server. It uses an internal sub-request to do the check, because it will reduce the performance of the server, so please use it carefully!

Note: All of these tests can be prefixed with an exclamation point ('! ') To achieve the reversal of test conditions.
3. You can also append a special tag [flags] after condpattern as the third parameter of the Rewritecond directive. Flags is a comma-delimited list of the following tokens:

' nocase| NC ' (ignoring case)
It makes the test ignore case, the extended teststring and Condpattern ' A-Z ' and ' A-Z ' are no different. This tag is used only for comparisons between TestString and Condpattern, and checks on file systems and child requests do not work.
' Ornext|or ' (or Next condition)
It combines the conditions of several rules in or, not the implied and. A typical example is as follows:

Rewritecond%{remote_host} ^host1.* [OR]
Rewritecond%{remote_host} ^host2.* [OR]
Rewritecond%{remote_host} ^host3.*
Rewriterule ... Rule set for these 3 hosts ... If you don't use this tag, you'll have to write three conditions/rules.

Example
If you want to rewrite the home page of a site by "User-agent:" in the request header, you can write:

Rewritecond  %{http_user_agent}  ^mozilla.*rewriterule  ^/$                 /homepage.max.html  [L]rewritecond  %{http_user_agent}  ^lynx.*rewriterule  ^/$                 /homepage.min.html  [l]rewriterule  ^/$                 /homepage.std.html  L

Explanation: If you use the browser recognition logo as ' Mozilla ', then you will get the homepage with maximum content (including frames, etc.). If you're using Lynx (terminal-based), you get a home page with minimal content (no table, etc.). If none of the above conditions are met (using a different browser), then you get a standard home page.

Apache Rewritecond Rules Parameter Introduction