use XML::LibXML;
my $parser = XML::LibXML->new();
my $doc = $parser->parse_string(<<"EOT");
<foo>
<blubb><b >username</b>
</blubb><b>nochn username</b>
</foo>
EOT

my @names = map { $_->textContent } $doc->findnodes("//b");

print for @names;