use 5.20.0;
use strict;

my $n = 4;
my $raw  = (1234567.56567);
my $orig = (1234567.56567 * $n);
say "raw real number:   $raw";
say "factored real nbr: $orig";
my $str = "This is a real number ${\($raw * $n)}.";
say $str;

(my $tybalt89 = $str) =~ s{ \d+ }{ $& =~ s/ \B (?= (?:\d{3})+ $ ) /,/xrg }xe;
say "tybalt89's with assignment and \\r tweak => \'$tybalt89\'";

(my $perlboy = (($raw) =~ s{ \d+\.?\d* }{ $& * 4 }erx )) =~ s{ \d+ }{
    $& =~ s/ (?<=\d) (?= (?:\d{3} )+ (?!\d) ) /,/xrg; }ex;
say "perlboy's => \'$perlboy\'";

(my $mixed = (($raw) =~ s{ \d+\.?\d* }{ $& * 4 }erx )) =~ s{ \d+ }{
    $& =~ s/ \B (?= (?:\d{3})+ $ ) /,/xrg }xe;
say "perboy's w/tybalt89's drop-in with \\r tweak => \'$mixed\'";

say "tybalt89's original regex, without assignment => ", ($str) =~ s{ \d+ }{ $& =~ s/ \B (?= (?:\d{3})+ $ ) /,/xgr }xer;

say "tybalt89's original regex, without assignment => ", (1234567.56567 * 4) =~ s{ \d+ }{ $& =~ s/ \B (?= (?:\d{3})+ $ ) /,/xgr }xer;

exit(0)
__END__