C:\Windows\system32>perl
use warnings;
use strict;

my $lib;                       # compile time file scope (declaration)
use lib $lib="XXX";            # compile time  use scope (assignment) 
print $lib;                    # run time     file scope (output)
__END__
XXX
C:\Windows\system32>

##</code><code>##

use warnings;
use strict;

my $lib;
print $lib;                    # prints XXX


use lib $lib="XXX";
__END__
XXX