This is the simple solution I've implemented, following Tanktalus's advice: 
my $stop;
my $speed = 0;
my $start = time;
while (<CONNS>) {
        $counter++;
        if ($counter =~ /00$/) {
                $stop = time;
                my $diff = $stop - $start;
                my $tdiff = ($diff == 0) ? 1 : $diff;

                $speed = sprintf("%.f", ($counter/$tdiff));
        }
        ... line processing ...
        print "Processed: $counter (at $speed lines/s)  \r";
}

[download]
Not so elegant or fast, but works. Thanks everyone!

In reply to Re: Live operations-per-second counter by acidmax
in thread Live operations-per-second counter by acidmax

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