my$re =
qr/
	begin
	(?:
		 (?> [^be]* )
		|(??{ $re })
		| [be]
	)*
	end
/x;

foreach (<DATA>)
{
	chomp;
	my @matches = $_ =~ /($re)/g;
	print qq(For "$_":\n\t);
	print (@matches ? join("*",@matches) : "no matches", "\n");
}
__DATA__
begin end
begin en
begin nd
begin begin end end
beginend
beginbeginbeginendendend
begin begin end begin begin end begin end end end
begin begin end begin  egin end begin end end end
begin end begin end