Take a look at LWP::Simple's (alt.) getstore or mirror functions.

my $url  = 'http://www.db.ucsd.edu/publications/xkeyword.pdf';
my $file = 'xkeyword.pdf';

unless ( is_success( mirror($url, $file) ) ) {
  warn "Couldn't download $url\n";
}
[download]

    --k.