update: Or, to insert newlines at the 10th position and avoid double spacing lines of 9 characters, perhaps this

use strict;
use warnings;
while (<DATA>) {
    my $var=$_;
    $var=~s/(.{9})/$1\n/;
    print "$var";
}

__DATA__
dgbjhdghjdfgjhd
dfgjdjfghjkdhgdfg
dgbhgdfjgjhgdfgdfg
ghgjgglhkdjghkdhgk

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In reply to Re^3: how to Insert a newline character in a sentence by ig
in thread how to Insert a newline character in a sentence by Anonymous Monk

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