c:\@Work\Perl>perl -wMstrict -le
"use Data::Dump qw(pp);
 ;;
 my $qr_string = q((?:\G(\w)\W{2}(\w)));
 my $qr = qr[$qr_string];
 ;;
 for my $s ('', qw(a--b  c--dE--F  g--hI--Jk--l)) {
   my @caps = $s =~ /$qr/g;
   print qq{'$s' -> }, pp \@caps;
   }
"
'' -> []
'a--b' -> ["a", "b"]
'c--dE--F' -> ["c", "d", "E", "F"]
'g--hI--Jk--l' -> ["g", "h", "I", "J", "k", "l"]

c:\@Work\Perl>perl -wMstrict -le
"use Data::Dump qw(pp);
 ;;
 my $qr_string = q((?:(\w)\W{2}(\w)));
 my $qr = qr[$qr_string];
 ;;
 for my $s ('', qw(a--b  c--dE--F  g--hI--Jk--l)) {
   my @caps = $s =~ /$qr/g;
   print qq{'$s' -> }, pp \@caps;
   }
"
'' -> []
'a--b' -> ["a", "b"]
'c--dE--F' -> ["c", "d", "E", "F"]
'g--hI--Jk--l' -> ["g", "h", "I", "J", "k", "l"]