You can localize $" to the empty string, or just use a scalar instead:

my @a = qw( a x z );
{
  local $" = "";
  while (<>) {
    print if /^[@a]{3}$/;  # /o might be good, too
  }
}
[download]

or

my @a = qw( a x z );
my $re = join '', @a;
while (<>) {
  print if /^$re$/;  # again, /o might help
}
[download]

_____________________________________________________
Jeff[japhy]Pinyan: Perl, regex, and perl hacker, who'd like a job (NYC-area)
s++=END;++y(;-P)}y js++=;shajsj<++y(p-q)}?print:??;