$foo = "line1line1line1line1line1line1line1line1
line2line2line2line2line2line2line2line2line2line2line2line2line2line2line2line2line2line2
line3line3line3line3line3line3line3line3";

if ($foo =~ /((?:^.{0,40})\n{1,4})/m)            
{ print "$1: OK\n\n"; } 


else
{print "$1: NOT OK\n\n";}