You need to provide more context, but I suspect you are trying to parse one line at a time, but match strings that span several lines.

I strongly suggest that you use a module such as XML::Twig to parse XML! Consider:

use strict;
use warnings;
use XML::Twig;

my $twig = XML::Twig->new (twig_roots => {content => \&contents});
my $xml = do {local $/; <DATA>};

$twig->parse ($xml);


sub contents {
    my ($twig, $contents) = @_;
    my @children = $contents->children ();
    my @wanted = qw(id title published);
    my $match = join '|', @wanted;
    my %params;

    for my $child (grep {$_->tag () =~ /^($match)$/} @children) {
        $params{$child->tag ()} = $child->text ();
    }

    print join "\t", @params{@wanted};
}


__DATA__
<data>
    <content>
        <id>http://gdata.youtube.com/feeds/api/videos/5InqyMvRZ8o/comm
+ents/7307D6E7F6E2D1B8
        </id>
        <published>2007-04-05T12:05:42.000-07:00
        </published>
        <updated>2007-04-05T12:05:42.000-07:00
        </updated>
        <category scheme='http://schemas.google.com/g/2005#kind' term=
+'http://gdata.youtube.com/schemas/2007#comment'/>
        <title type='text'>Fantastisk video,, ...
        </title>
         Keep up the good work. - jeg glder mig meget til at se flere 
+videoer fra dig..uper billeder du har fundet (:
    </content>
    <link rel='related' type='application/atom+xml' href='http://gdata
+.youtube.com/feeds/api/videos/5InqyMvRZ8o'/>
    <link rel='alternate' type='text/html' href='http://www.youtube.co
+m/watch?v=5InqyMvRZ8o'/>
    <link rel='self' type='application/atom+xml' href='http://gdata.yo
+utube.com/feeds/api/videos/5InqyMvRZ8o/comments/7307D6E7F6E2D1B8'/>
    <author>
        <name>cajaneil
        </name>
        <uri>http://gdata.youtube.com/feeds/api/users/cajaneil
        </uri>
    </author>
</data>
[download]

Prints:

http://gdata.youtube.com/feeds/api/videos/5InqyMvRZ8o/comments/7307D6E
+7F6E2D1B8
            Fantastisk video,, ...
            2007-04-05T12:05:42.000-07:00
[download]

Note that I altered the XML to make it valid and that I chose elements that exist as children of content for demonstration purposes. You will need to alter the code to suit what you are actually doing.