Question

I have a script that I wrote that can either be used on the command line or as a CGI script, and need to determine how the script was called so I can output a content-type header for web requests (and maybe some anti-cache headers too). My first thought is to check for the existance of http environment variables:

my $js = build_javascript();

if ( exists $ENV{HTTP_HOST} ) {
   print "Content-type: text/javascript\n\n";
}
print $js;

Is there a better way?

Answer 1

According to the CGI specification in RFC3875 (section 4.1.4.), the GATEWAY_INTERFACE environment variable would be the authoritative thing to check whether you are running in a CGI context:

4.1.4. GATEWAY_INTERFACE

The GATEWAY_INTERFACE variable MUST be set to the dialect of CGI
being used by the server to communicate with the script.