while (
    $line =~ 
      /
        (
          [^\[]*
        )
        (?:
          \[
          (
            (?:link|email|pdf)
            [^\]]*
          )
          \]
        )?
      /xg
  )
  {
    my $txt = $1;
    my $link = $2;
    if ($link){
      my ($type, $address, $txt) = split(/\|/, $link);
      # more stuff
    }
  }