sub foo {
   my ($cgi, ...) = @_;
   ...
   $cgi->...
   ...
}

sub main {
   my $cgi = ...;
   foo($cgi, ...);
}

main();

##</code><code>##

our $foo;

sub foo {
   my (...) = @_;
   ...
   $cgi->...
   ...
}

sub main {
   local $cgi = ...;
   foo(...);
}

main();