If you wish to avoid any modules, you can do it this way:

#!/usr/local/bin/perl
use strict;
use warnings;

my $var = "this is just a sample of a string, there is nothing really 
+important in the scalar, just a lot of text";

my $pos = 9;
while(( $pos = index($var, ' ', $pos)) > -1 ) {
    substr($var, $pos, 1) = "\n";
    $pos += 10;
}
print "\n$var\n";
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Just remember, TIMTOWTDI.

- - arden.