Since your records are separated by // you can change the value of $/, the input record separator so that instead of just one line, you will get a whole group at each iteration.

And with the /m modifier you can use ^ to mean the beginning of a line anywhere in your string.

Your input file seems to have a well defined format: "IDENTIFIER - value", so I think the easiest way to read it is to get all values in a hash, and then fetch the ones you need:

{
  local $/ = '//';
  while(my $record=<IN>)
  {
    my %values = $record =~ /^([-A-Z]+)\s+-\s+(.*)/mg;
    next unless exists $values{'UNIQUE-ID'} and exists $values{'ACCESS
+ION'};
    # Your code using $values{'UNIQUE-ID'} and other values here
  }
}
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