knoppix@Microknoppix:~$ perl -E '
> $str = q{one abc two abc three abc four};
> $sep = q{abc};
> say q{-} x 25;
> 
> @arr = split m{($sep)}, $str;
> say qq{Split on m{($sep)} into one array};
> say qq{  ->$_<-} for @arr;
> say  q{-} x 25;
> 
> push @{ $_ eq $sep ? \ @seps : \ @nums }, $_
>    for split m{($sep)}, $str;
> say qq{Split on m{($sep)} into two arrays};
> say  q{  Nums:};
> say qq{  ->$_<-} for @nums;
> say  q{  Seps:};
> say qq{  ->$_<-} for @seps;
> say  q{-} x 25;
> 
> @seps = (); @nums = ();
> push @{ $_ eq $sep ? \ @seps : \ @nums }, $_
>    for split m{\s+}, $str;
> say qq{Split on m{\\s+} into two arrays};
> say  q{  Nums:};
> say qq{  ->$_<-} for @nums;
> say  q{  Seps:};
> say qq{  ->$_<-} for @seps;
> say  q{-} x 25;'
-------------------------
Split on m{(abc)} into one array
  ->one <-
  ->abc<-
  -> two <-
  ->abc<-
  -> three <-
  ->abc<-
  -> four<-
-------------------------
Split on m{(abc)} into two arrays
  Nums:
  ->one <-
  -> two <-
  -> three <-
  -> four<-
  Seps:
  ->abc<-
  ->abc<-
  ->abc<-
-------------------------
Split on m{\s+} into two arrays
  Nums:
  ->one<-
  ->two<-
  ->three<-
  ->four<-
  Seps:
  ->abc<-
  ->abc<-
  ->abc<-
-------------------------
knoppix@Microknoppix:~$