>perl -wMstrict -le
"my $s =
   'aaaa bb ccccc ddd eeeeeee  ffff gg hhhhh iii jjjjjjj';
 ;;
 for my $ar ([2, 5, 3], [3, 7, 4], [4, 2],) {
   my $rx = rxg(@$ar);
   print $rx;
   my @groups = $s =~ m{ ($rx) }xmsg;
   print qq{'$_'  } for @groups;
   }
 ;;
 sub rxg {
   my ($rx) =
     map qr{ \b $_ \b }xms,
     join ' \s+ ',
     map qq{\\w{$_}},
     @_
     ;
   ;;
   return $rx;
   }
"
(?^msx: \b \w{2} \s+ \w{5} \s+ \w{3} \b )
'bb ccccc ddd'
'gg hhhhh iii'
(?^msx: \b \w{3} \s+ \w{7} \s+ \w{4} \b )
'ddd eeeeeee  ffff'
(?^msx: \b \w{4} \s+ \w{2} \b )
'aaaa bb'
'ffff gg'