Here is how I understand your question:

if getline is called with qw(foo bar baz bletch) you want:
- foo bar to be OK,
- toto tutu to be NOT OK,
- foo bar toto to be NOT OK,
- foo foo to be OK,
- an empty input to be OK.

sub getline
  { return unless @_;                              # caller don't want
+ checks
    my %valid_word= map { ( $_, 1) } @_;           # create a hash val
+id_word => 1
    my $line;
    chomp( $line = <>);
    my @word= split /\s/, $line;
    foreach my $word (@word)
      { return undef unless $valid_word{$word}; }  # return failure as
+ soon as a a bad word is found
    return $line;
  }
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Note that if you want to allow empty input lines you will have to test the result for undef, otherwise you can return 0 on failure or empty lines.