Most "speed" counters usually show the overall speed, not the current speed. Thus, you can even just print this out every x number of lines, and just divide the number of lines processed so far by the time elapsed (you may want to use Time::HiRes for that).

Or, rather than simply every x lines (where x may need to be large to keep from printing to STDOUT too often - STDOUT is actually very slow, so you don't want to waste too much time printing to the console), every x lines (where x can be much smaller) check the time (not HiRes) to see if the seconds have changed, and then print out (using HiRes, or not) the speed.

use Benchmark;

$t0 = new Benchmark;
# ... your code here ...
$t1 = new Benchmark;
$td = timediff($t1, $t0);
print "the code took:",timestr($td),"\n";
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It's part of the perl code core distribution, does a lot more, and doesn't need any extra code.

Code runs much slower with profiling turned on, so this method cannot be used to measure times (to say nothing of "in production").
--kap

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 $speed lines/s)  \r";
}
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if ($counter =~ /00$/) {
can be written as
if ($counter % 100 == 0) {
which saves perl from converting the number to a string and checking it against a regexp.

if ($counter % 100 == 0) {

Or even

unless ($counter % 100) {
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(But then it depends on how much one is familiar with such a construct - for me it is quite as intuitive as the former, but it's obvious that others' mileage may vary)

#!/usr/bin/perl

  use Term::ProgressBar 2.00;

  use constant MAX => 100_000;

  my $progress = Term::ProgressBar->new(MAX);

  for (0..MAX) {
    my $is_power = 0;
    for(my $i = 0; 2**$i <= $_; $i++) {
      $is_power = 1
        if 2**$i == $_;
    }

    if ( $is_power ) {
      $progress->update($_);
    }
  }
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Unfortunately, I don't know how many lines does this file contain. I have several other programs, where I could use it. Thanks a lot!

$setTimeStart = time;
$setCount = 0;
while (<IN>) {
   # process line here
   
   $setCount++;

   # show line speed for every 1000 lines so prints don't
   # slow you down so much
   if($setCount < 999) {
      $setCount = 0;
      $setTime = time - $setTimeStart;
      print "processing 1000 lines at " . $setTime/1000 . " per line\n
+";
      $setTimeStart = time;
   }
}
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use strict;

use Time::HiRes qw ( alarm time usleep sleep);

our $starttime;
our $lasttime;
our $linecount = 0;
our $lastlinecount = 0;

$SIG{ALRM} = sub {
        my $now = time;
        printf "\rline %d %8.1f avg lines per second %8.1f lines per s
+econd",
          $linecount, $linecount/($now - $starttime),
          ($linecount - $lastlinecount) 
            / ($now - $lasttime);
        $lasttime = time();
        $lastlinecount = $linecount;
    };

alarm(1, .5);
$| = 1;

$lasttime = $starttime = time();
while (1) {
    $linecount++;
    last if $linecount > 9999;
    usleep(0.001);
};
print "\n";
alarm(0);
$SIG{ALRM} = undef;
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And here is that threaded solution.

use strict;

use Config;
$Config{useithreads} or die "Recompile Perl with threads to run this p
+rogram.";

use threads;
use threads::shared;

use Time::HiRes qw ( time sleep);

our $starttime : shared;
our $linecount : shared = 0;
our $running : shared = 1;

sub progress {
    my $lasttime = $starttime;
    my $lastlinecount = 0;
    sleep(1);
    $| = 1;
    do {
        my $now = time();
        printf "\rline %d %8.1f avg lines per second %8.1f lines per s
+econd", $linecount, $linecount/($now - $starttime), ($linecount - $la
+stlinecount) / ($now - $lasttime);
        $lasttime = time();
        $lastlinecount = $linecount;
        sleep(.5);
    } while ($running);
};

$starttime = time();

our $thr1 = threads->new(\&progress);

while (1) {
    $linecount++;
    last if $linecount > 9999;
    sleep(0.001);
};
print "\n";
$running = 0;

$thr1->join();
[download]

-- gam3
A picture is worth a thousand words, but takes 200K.