Apache Module mod_include

Summary

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

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 in .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.

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.

Available Elements

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

<!--#element attribute=value attribute=value ... -->

The value will often be enclosed in double quotes, but single quotes (') and backticks (`) are also possible. 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. Note that the leading <!--# is one token and may not contain any whitespaces.

The allowed elements are listed in the following table:

SSI elements may be defined by modules other than mod_include. In fact, the exec element is provided by mod_cgi, and will only be available if this module is loaded.

The comment Element

This command doesn't output anything. Its only use is to add comments within a file. These comments are not printed.

This syntax is available in version 2.4.21 and later.

<!--#comment Blah Blah Blah -->

The config Element

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

echomsg (Apache 2.1 and later)

The value is a message that is sent back to the client if the echo element attempts to echo an undefined variable. This overrides any SSIUndefinedEcho directives.

<!--#config echomsg="[Value Undefined]" -->

errmsg

The value is a message that is sent back to the client if an error occurs while parsing the document. This overrides any SSIErrorMsg directives.

<!--#config errmsg="[Oops, something broke.]" -->

sizefmt

The value sets the format to be used when 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, for example a size of 1024 bytes will be printed as "1K".

<!--#config sizefmt="abbrev" -->

timefmt

The value is a string to be used by the strftime(3) library routine when printing dates.

<!--#config timefmt=""%R, %B %d, %Y"" -->

The echo Element

This command prints one of the include variables defined below. If the variable is unset, the result is determined by the SSIUndefinedEcho directive. Any dates printed are subject to the currently configured timefmt.

Attributes:

var

The value is the name of the variable to print.

decoding

Specifies whether Apache should strip an encoding from the variable before processing the variable further. The default is none, where no decoding will be done. If set to url, then URL decoding (also known as %-encoding; this is appropriate for use within URLs in links, etc.) will be performed. If set to urlencoded, application/x-www-form-urlencoded compatible encoding (found in query strings) will be stripped. If set to base64, base64 will be decoded, and if set to entity, HTML entity encoding will be stripped. Decoding is done prior to any further encoding on the variable. Multiple encodings can be stripped by specifying more than one comma separated encoding. The decoding setting will remain in effect until the next decoding attribute is encountered, or the element ends.

The decoding attribute must precede the corresponding var attribute to be effective.

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. If set to urlencoded, application/x-www-form-urlencoded compatible encoding will be performed instead, and should be used with query strings. If set to base64, base64 encoding 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, e.g. 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.

The encoding attribute must precede the corresponding var attribute to be effective.

In order to avoid cross-site scripting issues, you should always encode user supplied data.

Example

<!--#echo encoding="entity" var="QUERY_STRING" -->

The exec Element

The exec command executes a given shell command or CGI script. It requires mod_cgi to be present in the server. If Options IncludesNOEXEC is set, this command is completely disabled. The valid attributes are:

cgi

The value specifies a (%-encoded) URL-path to the CGI script. If the path does not begin with a slash (/), 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 Options ExecCGI).

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.

Example

<!--#exec cgi="/cgi-bin/example.cgi" -->

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. In particular, if you need to pass additional arguments to a CGI program, using the query string, this cannot be done with exec cgi, but can be done with include virtual, as shown here:

<!--#include virtual="/cgi-bin/example.cgi?argument=value" -->

cmd

The server will execute the given string using /bin/sh. The include variables are available to the command, in addition to the usual set of CGI variables.

The use of #include virtual is almost always prefered to using either #exec cgi or #exec cmd. The former (#include virtual) uses the standard Apache sub-request mechanism to include files or scripts. It is much better tested and maintained.

In addition, on some platforms, like Win32, and on unix when using suexec, you cannot pass arguments to a command in an exec directive, or otherwise include spaces in the command. Thus, while the following will work under a non-suexec configuration on unix, it will not produce the desired result under Win32, or when running suexec:

<!--#exec cmd="perl /path/to/perlscript arg1 arg2" -->

The fsize Element

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.

This file is <!--#fsize file="mod_include.html" --> bytes.

The value of file cannot start with a slash (/), nor can it contain ../ so as to refer to a file above the current directory or outside of the document root. Attempting to so will result in the error message: The given path was above the root path.

virtual

The value is a (%-encoded) URL-path. If it does not begin with a slash (/) then it is taken to be relative to the current document. Note, that this does not print the size of any CGI output, but the size of the CGI script itself.

This file is <!--#fsize virtual="/docs/mod/mod_include.html" --> bytes.

Note that in many cases these two are exactly the same thing. However, the file attribute doesn't respect URL-space aliases.

The flastmod Element

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.

The include Element

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 Options IncludesNOEXEC set, then only documents with a text MIME-type (text/plain, text/html etc.) will be included. 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, and may appear more than once in an include element; an inclusion is done for each attribute given to the include command in turn. 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. Therefore, you cannot include files that are outside of the document root, or above the current document in the directory structure. The virtual attribute should always be used in preference to this one.

virtual

The value is a (%-encoded) URL-path. 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.

If the specified URL is a CGI program, the program will be executed and its output inserted in place of the directive in the parsed file. You may include a query string in a CGI url:

<!--#include virtual="/cgi-bin/example.cgi?argument=value" -->

include virtual should be used in preference to exec cgi to include the output of CGI programs into an HTML document.

If the KeptBodySize directive is correctly configured and valid for this included file, attempts to POST requests to the enclosing HTML document will be passed through to subrequests as POST requests as well. Without the directive, all subrequests are processed as GET requests.

onerror

The value is a (%-encoded) URL-path which is shown should a previous attempt to include a file or virtual attribute failed. To be effective, this attribute must be specified after the file or virtual attributes being covered. If the attempt to include the onerror path fails, or if onerror is not specified, the default error message will be included.

# Simple example
<!--#include virtual="/not-exist.html" onerror="/error.html" -->

# Dedicated onerror paths
<!--#include virtual="/path-a.html" onerror="/error-a.html" virtual="/path-b.html" onerror="/error-b.html" -->

The printenv Element

This prints out a plain text listing of all existing variables and their values. Special characters are entity encoded (see the echo element for details) before being output. There are no attributes.

<pre> <!--#printenv --> </pre>

The set Element

This sets the value of a variable. Attributes:

var

The name of the variable to set.

value

The value to give a variable.

decoding

Specifies whether Apache should strip an encoding from the variable before processing the variable further. The default is none, where no decoding will be done. If set to url, urlencoded, base64 or entity, URL decoding, application/x-www-form-urlencoded decoding, base64 decoding or HTML entity decoding will be performed respectively. More than one decoding can be specified by separating with commas. The decoding setting will remain in effect until the next decoding attribute is encountered, or the element ends. The decoding attribute must precede the corresponding var attribute to be effective.

encoding

Specifies how Apache should encode special characters contained in the variable before setting them. The default is none, where no encoding will be done. If set to url, urlencoding, base64 or entity, URL encoding, application/x-www-form-urlencoded encoding, base64 encoding or HTML entity encoding will be performed respectively. More than one encoding can be specified by separating with commas. The encoding setting will remain in effect until the next encoding attribute is encountered, or the element ends. The encoding attribute must precede the corresponding var attribute to be effective. Encodings are applied after all decodings have been stripped.

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

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_ARGS

This variable contains the query string of the active SSI document, or the empty string if a query string is not included. For subrequests invoked through the include SSI directive, QUERY_STRING will represent the query string of the subrequest and DOCUMENT_ARGS will represent the query string of the SSI document. (Available in Apache HTTP Server 2.4.19 and later.)

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 the URL for the current document. Note also that if the URL is modified internally (e.g. by an alias or directoryindex), the modified URL is shown.

LAST_MODIFIED

The last modification date of the document requested by the user.

QUERY_STRING_UNESCAPED

If a query string is present in the request for the active SSI document, this variable contains the (%-decoded) query string, which is escaped for shell usage (special characters like & etc. are preceded by backslashes). It is not set if a query string is not present. Use DOCUMENT_ARGS if shell escaping is not desired.

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, echo, and set directives. If SSILegacyExprParser is set to on, substitution also occurs in the arguments to conditional operators. You can insert a literal dollar sign into the string using backslash quoting:

<!--#set var="cur" value="\$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, a 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".

Flow Control Elements

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 used to 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 a boolean expression which follows the ap_expr syntax. The syntax can be changed to be compatible with Apache HTTPD 2.2.x using SSILegacyExprParser.

The SSI variables set with the var element are exported into the request environment and can be accessed with the reqenv function. As a short-cut, the function name v is also available inside mod_include.

The below example will print "from local net" if client IP address belongs to the 10.0.0.0/8 subnet.

<!--#if expr='-R "10.0.0.0/8"' -->
 from local net
 <!--#else -->
 from somewhere else
 <!--#endif -->

The below example will print "foo is bar" if the variable foo is set to the value "bar".

<!--#if expr='v("foo") = "bar"' -->
 foo is bar
 <!--#endif -->

Legacy expression syntax

This section describes the syntax of the #if expr element if SSILegacyExprParser is set to on.

string

true if string is not empty

-A string

true if the URL represented by the string is accessible by configuration, false otherwise. This is useful where content on a page is to be hidden from users who are not authorized to view the URL, such as a link to that URL. Note that the URL is only tested for whether access would be granted, not whether the URL exists.

Example

<!--#if expr="-A /private" -->
 Click <a href="/private">here</a> to access private information.
 <!--#endif -->

string1 = string2
string1 == string2
string1 != string2

Compare string1 with string2. If string2 has the form /string2/ then it is treated as a regular expression. Regular expressions are implemented by the PCRE engine and have the same syntax as those in perl 5. Note that == is just an alias for = and behaves exactly the same way.

If you are matching positive (= or ==), you can capture grouped parts of the regular expression. The captured parts are stored in the special variables $1 .. $9. The whole string matched by the regular expression is stored in the special variable $0

Example

<!--#if expr="$QUERY_STRING = /^sid=([a-zA-Z0-9]+)/" -->
 <!--#set var="session" value="$1" -->
 <!--#endif -->

string1 < string2
string1 <= string2
string1 > string2
string1 >= string2

Compare string1 with string2. Note, that strings are compared literally (using strcmp(3)). Therefore the string "100" is less than "20".

( 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)" -->

The boolean operators && and || share the same priority. So if you want to bind such an operator more tightly, you should use parentheses.

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,

SSIEndTag tag

SSIEndTag "-->"

SSIEndTag "%>"

SSIErrorMsg message

SSIErrorMsg "[an error occurred while processing this directive]"

SSIErrorMsg "<!-- Error -->"

SSIETag on|off

SSIETag off

SSILastModified on|off

SSILastModified off

SSILegacyExprParser on|off

SSILegacyExprParser off

SSIStartTag tag

SSIStartTag "<!--#"

SSIStartTag "<%"
SSIEndTag   "%>"

<%printenv %>

SSITimeFormat formatstring

SSITimeFormat "%A, %d-%b-%Y %H:%M:%S %Z"

SSITimeFormat "%R, %B %d, %Y"

SSIUndefinedEcho string

SSIUndefinedEcho "(none)"

SSIUndefinedEcho "<!-- undef -->"

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