# Module mod_include

This module provides for server-parsed html documents.

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

## Summary

This module provides a handler 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.

## Directives

- XBitHack

See also: Options and AddHandler.

## 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
> <FilesMatch "\.shtml[.$]">
> SetOutputFilter INCLUDES
> </FilesMatch>`

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`

Alternatively the `XBitHack` directive can be used to parse normal (`text/html`) files, based on file permissions.

For backwards compatibility, documents with mime type `text/x-server-parsed-html` or `text/x-server-parsed-html3` will also be parsed (and the resulting output given the mime type `text/html`) as will documents with the handler `server-parsed`.

## Basic 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; 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: `<!--#printenv -->`
  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.

## 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 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 this, for example, when you `#include` a CGI that produces different output on each hit (or potentially depends on the hit).