How can I embed that into an UNIX Korn shell script?

Can't you sprintf to a variable, comma-munge it, and then print that?

$x = sprintf "%02d\/%02d\/%04d\ %02d\:%02d", $MM +1 , $DD , $YY + 1900
+, $hh, $mm;
$x =~ s/(\d)(?=(\d{3})+(\D|$))/$1\,/g;
print $x;
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You could lose the interim variable on the way to print, but it's easier to follow as above.