$ perl -MO=Deparse,-p -e 'print $fh $lsep if $rows++ and $lsep;'
((($rows++) and $lsep) and print($fh $lsep));
-e syntax OK
$
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So, increment $rows, and if that was previously true, and $lsep is also true, then print $lsep to filehandle $fh.

Deparse is your friend. Learn to use deparse.

-- Randal L. Schwartz, Perl hacker