DB<120> $str='xxx@@xx\@xx@abc\@xxx@efg@\xxx'
 => "xxx\@\@xx\\\@xx\@abc\\\@xxx\@efg\@\\xxx"


  DB<121> print ( defined $1 ? "$1\t" : "") while ( $str =~ m/ (?: [\\\@]{2} | ( \@\w+ ) | . ) /xg )
@abc	@efg	

  DB<122> grep { defined } $str =~ m/ (?: [\\\@]{2} | ( \@\w+ ) | . ) /xg
  => ("\@abc", "\@efg")

##</code><code>##

  DB<135> grep {defined} $str =~ m/ (?: [\\\@]{2}+ | ( [\\\@]\w+ ) | [^\\\@]+ ) /xg 
 => ("\@abc", "\@efg")