open F, $file;
close F;
# F is closed

{
    open my $fh, $file;
}
# $fh is closed

open F, $file;
exit 0;
# program is gone and F is closed

# closure
{
    my $fh;
    sub append {
        unless ( $fh ) { open $fh, $file }
    }
}
# closure means $fh is not destroyed, $fh remains open until program exit