if (! grep defined($_), @hash{ qw(A B C) } ) {
  # etc
}

[download]

UPDATE
merlyn is exactly right. Why you shouldn't try to answer with untested code while racing back to chatter...

In reply to Re (tilly) 1: Checking for defined-ness for a list by tilly
in thread Checking for defined-ness for a list by dragonchild

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