SSI(8) System Manager's Manual (smm) SSI(8)

ssi —
Server-Side-Includes CGI program

ssi

This is an external CGI program that provides the same functionality as the built-in server-side-includes feature in many HTTP daemons. It is written for use with thttpd(8) and merecat(8), but should be easy to adapt to other systems.
There are two ways to use this; the modern way of using a .shtml pattern in merecat.conf(5) to trigger the SSI script, which requires enabling the SSI module. Then there is the traditional thttpd(8) approach. We start with the relevant settings needed in merecat.conf: 
ssi { 
    enabled = true 
    pattern = "**.shtml"	# default 
    cgi-path = "cgi-bin/ssi"    # default, web server root is used 
}
The traditional thttpd way runs ssi as a simple CGI script, which requires placing the ssi binary in the web server CGI area, and enabling CGI. Then set up URLs with the path to the document to parse as the "pathinfo". That's the part of the URL that comes after the CGI program name. For example, if the URL to this program is: 

    http://www.acme.com/cgi-bin/ssi
and the url for the document is: 

    http://www.acme.com/users/wecoyote/doc.html
then the compound URL would be: 

    http://www.acme.com/cgi-bin/ssi/users/wecoyote/doc.html

The format description below is adapted from ⟨http://hoohoo.ncsa.uiuc.edu/docs/tutorials/includes.html⟩.
All directives are formatted as SGML comments within the document. This is in case the document should ever find itself in the client's hands unparsed. Each directive has the following format: 

    <!--#command tag1="value1" tag2="value2" -->
Note: the lack of space between the initial HTML comment start and the #command. This is explicitly stated in the standard and strictly enforced by all web servers implementing SSI.
Each command takes different arguments, most only accept one tag at a time. Here is a breakdown of the commands and their associated tags:
The config directive controls various aspects of the file parsing. There are two valid tags:
gives the server a new format to use when providing dates. This is a string compatible with the strftime(3) library call.
determines the formatting to be used when displaying the size of a file. 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.
overrides the default; “[an error occurred while processing this directive]”
Inserts the text of another document into the parsed document. The inserted file is parsed recursively, so it can contain server-side-include directives too. This command accepts two tags:
Gives a virtual path to a document on the server.
Gives a pathname relative to the current directory. ../ cannot be used in this pathname, nor can absolute paths be used.
Prints the value of one of the include variables (defined below). Any dates are printed subject to the currently configured timefmt. The only valid tag to this command is var, whose value is the name of the variable you wish to echo.
prints the size of the specified file, subject to the sizefmt parameter to the config command. Valid tags are the same as with the include command.
prints the last modification date of the specified file, subject to the formatting preference given by the timefmt parameter to config. Valid tags are the same as with the include command.

A number of variables are made available to parsed documents. In addition to the CGI variable set, the following variables are made available:
The current filename.
The virtual path to this document (such as /~robm/foo.shtml).
The unescaped version of any search query the client sent.
The current date, local time zone. Subject to the timefmt parameter to the config command.
Same as DATE_LOCAL but in Greenwich mean time (GMT).
The last modification date of the current document. Subject to timefmt like the others.

merecat(8), merecat.conf(5), strftime(3)


Jef Poskanzer ⟨jef@mail.acme.com⟩ wrote the original for use with thttpd.
Joachim Nilsson ⟨troglobit@gmail.com⟩ added minor features and a trigger in merecat for .shtml pages.

Does not implement all "modern" SSI directives are supported. E.g., exec cgi and exec cmd or any control directives like if, elif, else, endif, etc. Patches and pull-requests are welcome :)
August 3, 2019 merecat (2.32)