I'm a little confused about what you are trying to do here. If it's your intention to process the SSI-directives while your CGI-script reads the file and prints it to STDOUT, it won't work.
The processing of the SSI directives will be done by the webserver only because it detects the file-extension .shtml. Since the server now processes your CGI script (ending in .cgi or .pl), it does not know that it is supposed to interpret the directives...

HTH

Jouke

Originally posted as a Categorized Answer.