my @block;
my $reject;
while (<>)
{
    if (/^interface/ .. /!/)
    {
        if (/shutdown/)
        {
            $reject = 1;
            @block = ();
        }
        if (not $reject)
        {
            unshift @block, $_;
        }
    }
    else
    {
        $reject = 0;
        if (@block > 0)
        {
            print @block;
            @block = ();
        }
    }
}