So this perl version did not like the replacement s/(.{20}) /$1\n/gr

Indeed not. 5.6.1 is far too old for the /r modifier. Pre-copy instead. eg:

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

my $in = 'Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed
+ do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut en
+im ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut
+ aliquip ex ea commodo consequat. Duis aute irure dolor in reprehende
+rit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. E
+xcepteur sint occaecat cupidatat non proident, sunt in culpa qui offi
+cia deserunt mollit anim id est laborum.';

(my $out = $in) =~ s/(.{20}) /$1\n/g;
print "In:\n$in\n\nOUT:\n$out\n";
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