Module mod_include

This module provides for server-parsed html documents.

Status: Base
Source File: mod_include.c
Module Identifier: include_module

Summary

This module provides a filter which will process files before they are sent to the client. The processing is controlled by specially formated SGML comments, referred to as elements. These elements allow conditional text, the inclusion other files or programs, as well as the setting and printing of environment variables.

See also: Options, SetOutputFilter, and AcceptPathInfo.

Enabling Server-Side Includes

Server Side Includes are implemented by the INCLUDES filter. If documents containing server-side include directives are given the extension .shtml, the following directives will make Apache parse them and assign the resulting document the mime type of text/html:

AddType text/html .shtml AddOutputFilter INCLUDES .shtml

The following directive must be given for the directories containing the shtml files (typically in a <Directory> section, but this directive is also valid .htaccess files if AllowOverride Options is set):

Options +Includes

For backwards compatibility, the server-parsed handler also activates the INCLUDES filter. As well, Apache will activate the INCLUDES filter for any document with mime type text/x-server-parsed-html or text/x-server-parsed-html3 (and the resulting output will have the mime type text/html).

For more information, see our Tutorial on Server Side Includes.

Basic Elements

The document is parsed as an HTML document, with special commands embedded as SGML comments. A command has the syntax:

The value will often be enclosed in double quotes; many commands only allow a single attribute-value pair. Note that the comment terminator (-->) should be preceded by whitespace to ensure that it isn't considered part of an SSI token.

The allowed elements are:

config

This command controls various aspects of the parsing. The valid attributes are:

errmsg: The value is a message that is sent back to the client if an error occurs whilst parsing the document.
sizefmt: The value sets the format to be used which displaying the size of a file. Valid values are bytes for a count in bytes, or abbrev for a count in Kb or Mb as appropriate.
timefmt: The value is a string to be used by the strftime(3) library routine when printing dates.

echo

This command prints one of the include variables, defined below. If the variable is unset, it is printed as (none). Any dates printed are subject to the currently configured timefmt. Attributes:

var: The value is the name of the variable to print.
encoding: Specifies how Apache should encode special characters contained in the variable before outputting them. If set to "none", no encoding will be done. If set to "url", then URL encoding (also known as %-encoding; this is appropriate for use within URLs in links, etc.) will be performed. At the start of an echo element, the default is set to "entity", resulting in entity encoding (which is appropriate in the context of a block-level HTML element, eg. a paragraph of text). This can be changed by adding an encoding attribute, which will remain in effect until the next encoding attribute is encountered or the element ends, whichever comes first. Note that the encoding attribute must precede the corresponding var attribute to be effective, and that only special characters as defined in the ISO-8859-1 character encoding will be encoded. This encoding process may not have the desired result if a different character encoding is in use. Apache 1.3.12 and above; previous versions do no encoding.

exec

The exec command executes a given shell command or CGI script. The IncludesNOEXEC Option disables this command completely. The valid attributes are:

cgi

The value specifies a (%-encoded) URL relative path to the CGI script. If the path does not begin with a (/), then it is taken to be relative to the current document. The document referenced by this path is invoked as a CGI script, even if the server would not normally recognize it as such. However, the directory containing the script must be enabled for CGI scripts (with ScriptAlias or the ExecCGI Option).

The CGI script is given the PATH_INFO and query string (QUERY_STRING) of the original request from the client; these cannot be specified in the URL path. The include variables will be available to the script in addition to the standard CGI environment.

If the script returns a Location: header instead of output, then this will be translated into an HTML anchor.

The include virtual element should be used in preference to exec cgi.

cmd

The server will execute the given string using /bin/sh. The include variables are available to the command.

fsize

This command prints the size of the specified file, subject to the sizefmt format specification. Attributes:

file: The value is a path relative to the directory containing the current document being parsed.
virtual: The value is a (%-encoded) URL-path relative to the current document being parsed. If it does not begin with a slash (/) then it is taken to be relative to the current document.

flastmod

This command prints the last modification date of the specified file, subject to the timefmt format specification. The attributes are the same as for the fsize command.

include

This command inserts the text of another document or file into the parsed file. Any included file is subject to the usual access control. If the directory containing the parsed file has the Option IncludesNOEXEC set, and the including the document would cause a program to be executed, then it will not be included; this prevents the execution of CGI scripts. Otherwise CGI scripts are invoked as normal using the complete URL given in the command, including any query string.

An attribute defines the location of the document; the inclusion is done for each attribute given to the include command. The valid attributes are:

file: The value is a path relative to the directory containing the current document being parsed. It cannot contain ../, nor can it be an absolute path. The virtual attribute should always be used in preference to this one.
virtual: The value is a (%-encoded) URL relative to the current document being parsed. The URL cannot contain a scheme or hostname, only a path and an optional query string. If it does not begin with a slash (/) then it is taken to be relative to the current document.

A URL is constructed from the attribute, and the output the server would return if the URL were accessed by the client is included in the parsed output. Thus included files can be nested.

printenv

This prints out a listing of all existing variables and their values. Starting with Apache 1.3.12, special characters are entity encoded (see the echo element for details) before being output. No attributes.

For example: 

Apache 1.2 and above.

set

This sets the value of a variable. Attributes:

var: The name of the variable to set.
value: The value to give a variable.

For example:

<!--#set var="category" value="help"
        -->

Apache 1.2 and above.

Include Variables

In addition to the variables in the standard CGI environment, these are available for the echo command, for if and elif, and to any program invoked by the document.

DATE_GMT: The current date in Greenwich Mean Time.
DATE_LOCAL: The current date in the local time zone.
DOCUMENT_NAME: The filename (excluding directories) of the document requested by the user.
DOCUMENT_URI: The (%-decoded) URL path of the document requested by the user. Note that in the case of nested include files, this is not then URL for the current document.
LAST_MODIFIED: The last modification date of the document requested by the user.

Variable Substitution

Variable substitution is done within quoted strings in most cases where they may reasonably occur as an argument to an SSI directive. This includes the config, exec, flastmod, fsize, include, and set directives, as well as the arguments to conditional operators. You can insert a literal dollar sign into the string using backslash quoting:

    <!--#if expr="$a = \$test" -->

If a variable reference needs to be substituted in the middle of a character sequence that might otherwise be considered a valid identifier in its own right, it can be disambiguated by enclosing the reference in braces, à la shell substitution:

    <!--#set var="Zed" value="${REMOTE_HOST}_${REQUEST_METHOD}" -->

This will result in the Zed variable being set to "X_Y" if REMOTE_HOST is "X" and REQUEST_METHOD is "Y".

EXAMPLE: the below example will print "in foo" if the DOCUMENT_URI is /foo/file.html, "in bar" if it is /bar/file.html and "in neither" otherwise:

    <!--#if expr="\"$DOCUMENT_URI\" = \"/foo/file.html\"" -->
    in foo
    <!--#elif expr="\"$DOCUMENT_URI\" = \"/bar/file.html\"" -->
    in bar
    <!--#else -->
    in neither
    <!--#endif -->

Flow Control Elements

These are available in Apache 1.2 and above. The basic flow control elements are:

    <!--#if expr="test_condition" -->
    <!--#elif expr="test_condition" -->
    <!--#else -->
    <!--#endif -->

The if element works like an if statement in a programming language. The test condition is evaluated and if the result is true, then the text until the next elif, else. or endif element is included in the output stream.

The elif or else statements are be used the put text into the output stream if the original test_condition was false. These elements are optional.

The endif element ends the if element and is required.

test_condition is one of the following:

string: true if string is not empty
string1 = string2 string1 != string2 string1 < string2 string1 <= string2 string1 > string2 string1 >= string2: Compare string1 with string 2. If string2 has the form /string/ then it is compared as a regular expression. Regular expressions have the same syntax as those found in the Unix egrep command.
( test_condition ): true if test_condition is true
! test_condition: true if test_condition is false
test_condition1 && test_condition2: true if both test_condition1 and test_condition2 are true
test_condition1 || test_condition2: true if either test_condition1 or test_condition2 is true

"=" and "!=" bind more tightly than "&&" and "||". "!" binds most tightly. Thus, the following are equivalent:

    <!--#if expr="$a = test1 && $b = test2" -->
    <!--#if expr="($a = test1) && ($b = test2)" -->

Anything that's not recognized as a variable or an operator is treated as a string. Strings can also be quoted: 'string'. Unquoted strings can't contain whitespace (blanks and tabs) because it is used to separate tokens such as variables. If multiple strings are found in a row, they are concatenated using blanks. So,

     string1    string2  results in string1 string2
    'string1    string2' results in string1    string2

Using Server Side Includes for ErrorDocuments

There is a document which describes how to use the features of mod_include to offer internationalized customized server error documents.

PATH_INFO with Server Side Includes

Files processed for server-side includes no longer accept requests with PATH_INFO (trailing pathname information) by default. You can use the AcceptPathInfo directive to configure the server to accept requests with PATH_INFO.

SSIEndTag directive

Syntax: SSIEndTag tag
Default: SSIEndTag "-->"
Context: server config, virtual host
Status: Base
Module: mod_include
Compatibility: Available in version 2.0.30 and later.

This directive changes the string that mod_include looks for to mark the end of a include command.

SSIErrorMsg directive

Syntax: SSIErrorMsg message
Default: SSIErrorMsg "[an error occurred while processing this directive]"
Context: server config, virtual host, directory, .htaccess
Status: Base
Module: mod_include
Compatibility: Available in version 2.0.30 and later.

The SSIErrorMsg directive changes the error message displayed when mod_include encounters an error. For production servers you may consider changing the default error message to "<-- Error -->" so that the message is not presented to the user.

This directive has the same effect as the <--#config errmsg=message --> element.

SSIStartTag directive

Syntax: SSIStartTag tag
Default: SSIStartTag "<--!"
Context: server config, virtual host
Status: Base
Module: mod_include
Compatibility: Available in version 2.0.30 and later.

This directive changes the string that mod_include looks for to mark an include element to process.

You may want to use this option if have 2 servers parsing the output of a file each processing different commands (possibly at different times).

SSITimeFormat directive

Syntax: SSITimeFormat formatstring
Default: SSITimeFormat "%A, %d-%b-%Y %H:%M:%S %Z"
Context: server config, virtual host, directory, .htaccess
Status: Base
Module: mod_include
Compatibility: Available in version 2.0.30 and later.

This directive changes the format in which date strings are displayed when echoing DATE environment variables. The formatstring is as in strftime(3) from the C standard library.

This directive has the same effect as the <--#config timefmt=formatstring --> element.

XBitHack directive

Syntax: XBitHack on|off|full
Default:

XBitHack
    off

Context: server config, virtual host, directory, .htaccess
Override: Options
Status: Base
Module: mod_include

The XBitHack directives controls the parsing of ordinary html documents. This directive only affects files associated with the MIME type text/html. XBitHack can take on the following values:

off: No special treatment of executable files.
on: Any text/html file that has the user-execute bit set will be treated as a server-parsed html document.
full: As for on but also test the group-execute bit. If it is set, then set the Last-modified date of the returned file to be the last modified time of the file. If it is not set, then no last-modified date is sent. Setting this bit allows clients and proxies to cache the result of the request.
Note: you would not want to use the full option, unless you assure the group-execute bit is unset for every SSI script which might #include a CGI or otherwise produces different output on each hit (or could potentially change on subsequent requests).