Or if you want to do the same thing in both cases, you can do with only a single evaluation:

if(
    $ENV{REQUEST_URI} =~ $regex
        ? $ENV{REQUEST_URI} =~ $regex2
        : 1
) {
    # ...
}
[download]

Which reads a lot less awkwardly using $_.

local $_ = $ENV{REQUEST_URI};
if(/$regex/ ? /$regex2/ : 1) {
    # ...
}
[download]

In other words, if matching $regex succeed, then it depends on whether it matches $regex2, if it failed, then it's always true.

Makeshifts last the longest.