Environment variables are used in CGI scripts to represent information that is updated by the Web server when the scripts run. Using environment variables, scripts can get and use up-to-date information without having to store that information themselves.
In addition to the standard environment variables, the following three environment variables are available to all scripts on your site:
SITE_ROOT.
The root path of your siteSITE_CGIROOT.
The top level CGI path of your siteSITE_HTMLROOT.
The top level HTML CGI path of your siteYou can use these variables in your CGI scripts to avoid hard-coding directory path names. This ensures that path names are always correct, even if those path names change.