print $_, /(x(.*)x(??{ '.{'.length($2).'}' })x)/
	? " matches, \$1 = $1\n" : " doesn't match\n"
		for qw/ xxx x.x.x x12x..x x123x...x x1x2x...x
			x123x.x.x x12x1x ax1x2xbx34x56xc /;

__END__

xxx matches, $1 = xxx
x.x.x matches, $1 = x.x.x
x12x..x matches, $1 = x12x..x
x123x...x matches, $1 = x123x...x
x1x2x...x matches, $1 = x1x2x...x
x123x.x.x matches, $1 = x123x.x.x
x12x1x doesn't match
ax1x2xbx34x56xc matches, $1 = x1x2xbx34x56x