Try the following code:

chomp( my $header = <> );
my @field_names = split /\s+/, $header;
my $expected_field_count = scalar(@field_names);

while( <>) {
    chomp;
    my @fields = split /\s+/;
    my $field_count = scalar(@fields);

    if ($field_count > $expected_field_count)) {
        warn "Input error: <<<$_>>> has $field_count fields, but $expe
+cted_field_count were expected.\n",
             'Fields obtained were: (', join(')(', @fields), ')';
    }

    foreach my $index (0 .. $#fields ) {
        print "$field_names[$index]:  $fields[$index]\n"
    }
}
[download]

You will find at least one of your lines of input produces a rather verbose warning. It is likely that this is the result of not handling some special case as you unpack your input. Often the best way of dealing with these sorts of issues is to use an input parser that is known to handle edge cases predictably. Text::CSV or its brother Text::CSV_XS would be a good choice. However, you're working on "Exercise_9_6", so it could be your instructor prefers that you not use an off-the-shelf CSV parser. In that case, you'll have to explore the fun of escaping field delimiters through metacharacters such as backslash, or through quote constructs. That's not much fun, which is why we like to use off-the-shelf parsers.

While you're here, you should write tests for your parser, and this edge case should be included in your tests.