The "eq" does not work the same as regular expression pattern matching. The latter is much more powerful.

Your question:

what would a wild card for :
if ($ENV{REMOTE_ADDR} eq '180.76.6.') {

is not specific enough. The answer depends on what you want to match against.
For example, to match any digits (actually, between 1 and 3 digits) after the last ".", but require the initial 3 octets to be identical to what is specified, use:

if ($ENV{REMOTE_ADDR} =~/180\.76\.6\.\d{1,3}/) {
[download]

My previous post shows a somewhat more flexible regular expression that allows but does not require leading zeros in an octet.

However, as afoken (++) pointed out, this may be too much flexibility if the value you are checking for comes from a "trusted" source, like the CGI module.