[... use use use use use use ...]
my %opt = (min => 10, max => 15,);
GetOptions(\%opt, qw(input=s output=s min:i max:i)) or pod2usage(2);

{
    my $in  = IO::File->new('-' eq $opt{input}  ? '<-' : ($opt{input},  'r'))
        or die "could not open $opt{input} for reading: $!\n";
    my $out = IO::File->new('-' eq $opt{output} ? '>-' : ($opt{output}, 'w'))
        or die "could not open $opt{output} for writing: $!\n";

    [while ...]
}
# Handles hier automatisch geschlossen, da Ende des Gültigkeitsbereichs.