@matches = 
[ "LISTOP",
  "OP",
  "COP",
  "BINOP",
  [ "LOOP",
    [ "OP",
      "UNOP",
      [ "OP",
	"UNOP",
	[ "SVOP" ], ], ],
    "UNOP",
    [ "LOGOP",
      [ "OP",
	"LISTOP",
	[ "COP",
	  "LISTOP",
	  [ "OP",
	    "UNOP",
	    [ "SVOP" ], ],
	  "OP",
	  "COP" ], ], ], ], ]
  =~ m[(SVOP\[{[-1,-1]}UNOP)]g;

print Dumper(\@matches);
$VAR => [# match 0
	 [ "UNOP",
	   [ "SVOP" ] ],
	 # Match 1
	 [ "UNOP",
	   [ "SVOP" ] ] ];

# empty those end SVOP strings
s[(?<=UNOP\[{[0,1],[1,1]})SVOP][];