Use the SERVER_NAME environment variable

The script has access to the domain name of the virtual server via $ENV{'SERVER_NAME'}.

Use this environment variable instead of hard-wiring the server name throughout the code:

$myserver = $ENV{'HTTP_HOST'} || $ENV{'SERVER_NAME'};

By using SERVER_NAME, your CGI script will not be sensitive if you change the domain name at a later date.

Use the DOCUMENT_ROOT environment variable

Avoid using absolute paths to your data files (i.e. /usr/home/yourname.com/file.txt). Use $ENV{'DOCUMENT_ROOT'} instead. This variable is of the form: /usr/home/yourname.com/htdocs

By using DOCUMENT_ROOT, your CGI script will not be sensitive to changes in directory structure, or changes in domain name. The following table shows the most common paths in terms of DOCUMENT_ROOT:

Home directory	Absolute path: /usr/home/yourname.com Recommended path: $ENV{'DOCUMENT_ROOT'}/.. Seasoned approach: $homedir = $ENV{'DOCUMENT_ROOT'}; $homedir =~ s#/htdocs$## || die;
Document root	Absolute path: /usr/home/yourname.com/htdocs Recommended path: $ENV{'DOCUMENT_ROOT'}
CGI-BIN directory	Absolute path: /usr/home/yourname.com/htdocs/cgi-bin Recommended path: $ENV{'DOCUMENT_ROOT'}/cgi-bin

 

Use the SCRIPT_NAME environment variable

A common mistake is to hard-wire the script name throughout the code, or via a configuration parameter. However, this is unnecessary. The script has access to its name as $ENV{'SCRIPT_NAME'}:

$myserver = $ENV{'HTTP_HOST'} || $ENV{'SERVER_NAME'};
$myurl = "http://$myserver$ENV{'SCRIPT_NAME'}";

By using SCRIPT_NAME, your CGI script will not be sensitive if you choose to rename it at a later date.

 

Use the HTTPS environment variable

Don't hard-wire the "http://" into the script, especially if you plan to use secure server. Use $ENV{'HTTPS'} instead:

$myserver = $ENV{'HTTP_HOST'} || $ENV{'SERVER_NAME'};
$myhttp = $ENV{'HTTPS'} ? "https://" : "http://";
$myurl = "$myhttp$myserver$ENV{'SCRIPT_NAME'}";

By using HTTPS, your CGI script will not be sensitive if you choose to move it to/from a secure server environment.

 

Use other environment variables

Many other environment variables are available for your use. By using environment variables instead of hard-wiring variables, you will be able to seamlessly move scripts between servers, between drives, to/from a secure server environment, and even rename the script, all without the need to edit the script.

For a list of environment variables available to your CGI script, please visit /cgi-bin/env.pl which is pre-installed into your /cgi-bin directory.