I'm not sure exactly what you want to do here, but as it stands, this part of your code doesn't do anything.

sub getgold {
    my $start= index $GoldLine, ":" + 2;
    return substr $start, length $line; #changed 'result' to 'return'
}
getgold;
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return ends the subroutine and passes back it's arguments. So, for this to do something, you will want to get the result of the subroutine by saying $result = getgold; or some such.

So now, $result will contain a string from 2 characters after the ':' in $GoldLine to the end.

Its good programming practice to use parentheses on funtions to make it clear what you're doing. So, you should say substr($start, length $line) instead of substr $start, length $line to be more explicit.

Update: Oops, that probably isn't doing what you want. The first argument to substr is the string that you're operating on. So, assuming you want to find a substring of $GoldLine, you would really want to say substr($GoldLine, $start, length $line). Also, if you omit that 3rd parameter, substr returns everything until the end of the string. So, you can just say substr($GoldLine, $start).

Also, if you want to see errors in your web browser instead of the dreaded "500 Server Error", add the line use CGI::Carp qw/fatalsToBrowser/; at the top of your script. Note that this only prints runtime errors; compiliation errors will give a rather unhelpful 'compilation failed' message.