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:

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):

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.

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, 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 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.

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.

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".

timefmt

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

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.

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, 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, and 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.

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

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.

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.

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; 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. 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.

The printenv Element

This prints out a 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.

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.

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 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, this variable contains the (%-decoded) query string, which is escaped for shell usage (special characters like & etc. are preceded by backslashes).

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, as well as the arguments to conditional operators. You can insert a literal dollar sign into the string using backslash quoting:

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:

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

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:

Flow Control Elements

The basic flow control elements are:

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 one of the following:

string

true if string is not empty

-A string

true if the URL represented by the string is accessible by configuration, false otherwise. This test only has an effect if SSIEnableAccess is on. 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.

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:

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,

SSIEnableAccess Directive

The SSIEnableAccess directive controls whether the -A test is enabled during conditional flow control processing. SSIEnableAccess can take on the following values:

off

<!--#if expr="-A /foo"--> will be interpreted as a series of string and regular expression tokens, the -A has no special meaning.

on

<!--#if expr="-A /foo"--> will evaluate to false if the URL /foo is inaccessible by configuration, or true otherwise.

SSIEndTag Directive

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

See also

• SSIStartTag

SSIErrorMsg Directive

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.

SSIETag Directive

Under normal circumstances, a file filtered by mod_include may contain elements that are either dynamically generated, or that may have changed independently of the original file. As a result, by default the server is asked not to generate an ETag header for the response by adding no-etag to the request notes.

The SSIETag directive suppresses this behaviour, and allows the server to generate an ETag header. This can be used to enable caching of the output. Note that a backend server or dynamic content generator may generate an ETag of its own, ignoring no-etag, and this ETag will be passed by mod_include regardless of the value of this setting. SSIETag can take on the following values:

off

no-etag will be added to the request notes, and the server is asked not to generate an ETag. Where a server ignores the value of no-etag and generates an ETag anyway, the ETag will be respected.

on

Existing ETags will be respected, and ETags generated by the server will be passed on in the response.

SSILastModified Directive

Under normal circumstances, a file filtered by mod_include may contain elements that are either dynamically generated, or that may have changed independently of the original file. As a result, by default the Last-Modified header is stripped from the response.

The SSILastModified directive overrides this behaviour, and allows the Last-Modified header to be respected if already present, or set if the header is not already present. This can be used to enable caching of the output. SSILastModified can take on the following values:

off

The Last-Modified header will be stripped from responses, unless the XBitHack directive is set to full as described below.

on

The Last-Modified header will be respected if already present in a response, and added to the response if the response is a file and the header is missing. The SSILastModified directive takes precedence over XBitHack.

SSIStartTag Directive

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 you have 2 servers parsing the output of a file each processing different commands (possibly at different times).

The example given above, which also specifies a matching SSIEndTag, will allow you to use SSI directives as shown in the example below:

See also

• SSIEndTag

SSITimeFormat Directive

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.

The above directive would cause times to be displayed in the format "22:26, June 14, 2002".

SSIUndefinedEcho Directive

This directive changes the string that mod_include displays when a variable is not set and "echoed".

XBitHack Directive

The XBitHack directive 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).

The SSILastModified directive takes precedence over the XBitHack directive when SSILastModified is set to on.