What are "server side includes" and how do I use them?

Penn Engineering CETS Answers

What are "server side includes" and how do I use them?

NCSA httpd, which is the program that serves Eniac's World-Wide Web pages, allows users to create documents which provide simple information to clients on the fly. Such information can include the current date, the file's last modification date, etc. These features of our httpd are called server side includes.

Server side includes can be put into a regular WWW document, but a file containing server side includes needs to have a .shtml extension, instead of the standard .html one. If the filename of a document does not end on .shtml, all server side include directives will be ignored!

You should be aware that documents containing server side includes take longer to access, since httpd needs to parse the whole document while looking for server side include directives. Please be selective when creating .shtml files -- unnecessary use of server side includes might slow down the server, affecting availability of yours and other users' pages.

Using server side includes

All server side include directives have the following format:

<!--#command argument="value">

Each command takes different arguments. Note that there is no space between the dashes and the # character. Here's the breakdown of supported commands and their associated arguments:

include will insert the text of a WWW document into the parsed document. Any included file is subject to the usual access control.
The only supported argument to the include command is file, which specifies a path to an HTML document relevant to the current directory. Neither "..", not an absulute path can be used. For example, to include contents of the file http://www.seas.upenn.edu/cets/answers/ns-httpd/include_example.html I used the following directive:
```

       
```
which resulted in the following getting inserted into this document:
This text comes from the file include_example.html
echo prints the value of one of the include variables. A number of variables are made available to parsed documents. Some of these variables are described in NCSA's CGI Environment Variables listing. Also, the following variables are available:
- DOCUMENT_NAME: The current filename.
- DOCUMENT_URI: The virtual path to this document (such as /~user/doc.shtml).
- QUERY_STRING_UNESCAPED: The unescaped version of any search query the client sent, with all shell-special characters escaped with \.
- DATE_LOCAL: The current date, local time zone.
- DATE_GMT: Same as DATE_LOCAL but in Greenwich mean time.
- LAST_MODIFIED: The last modification date of the current document.
The only valid argument to the echo command is var, whose value is the name of the variable you wish to echo. For example, specifying
Displays:
fsize prints the size of the specified file. Valid tags are the same as with the include command.
flastmod prints the last modification date of the specified file. Valid tags are the same as with the include command.
config controls various aspects of the file parsing. There are two valid arguments:
- timefmt gives the server a new format to use when providing dates, such as through the flastmod command. This is a string compatible with the strftime library call under most versions of UNIX. (See "man strftime" for details.)
- sizefmt determines the formatting to be used when displaying the size of a file, such as through the fsize command. Valid choices are bytes, for a formatted byte count (formatted as 1,234,567), or abbrev for an abbreviated version displaying the number of kilobytes or megabytes the file occupies.

Information about server side includes was taken from NCSA's server side includes tutorial, which also describes some commands that are not available on Eniac, such as the exec command.