#!/usr/bin/perl -wT

if ($ENV{'HTTP_ACCEPT'} =~ /application\/xhtml\+xml/)
{
    print "content-type:application/xhtml+xml; charset=utf-8\n\n";
}else{
    print "content-type:text/html; charset=utf-8\n\n";
}

##</code><code>##

#!/usr/bin/perl -wT

unless ($ENV{'HTTP_ACCEPT'} =~ /application\/xhtml\+xml/)
{
	print "content-type:text/html; charset=utf-8\n\n";
}else{
	print "content-type:application/xhtml+xml; charset=utf-8\n\n";
}

##</code><code>##

Use of uninitialized value $ENV{"HTTP_ACCEPT"}...