Hi, Just try this

$x = "piyushpiyushpiyushpiyushpiyushpiyushpiyushpiyushpiyushpiyushpiyu
+shpiyushpiyushpiyushpiyush";
$x =~ s#(.{64})#$1\n#gsi;
print $x;

o/p: 
piyushpiyushpiyushpiyushpiyushpiyushpiyushpiyushpiyushpiyushpiyu
shpiyushpiyushpiyushpiyush
[download]

Regards,

Gubendran.L