#!/usr/bin/env perl
# $Id: proc-fd-pos,v 1.1 2013/11/18 06:10:58 friedman Exp $

use strict;
use Symbol;

sub main
{
  my ($pid, $fd) = @_;
  my $name = "/proc/$pid/fdinfo/$fd";

  my $fh = gensym;
  open ($fh, $name) || die "$name: $!\n";

  $| = 1;

  my $interval = $_[2] || 10;
  my $last = 0;
  do
    {
      seek ($fh, 0, 0);
      local $_ = <$fh>;
      my $pos = $1 if /^pos:\s+(\d+)/;
      printf ("\r%u  %.02fk  %.02fm  %.02fg  (%.02f m/s) ",
              $pos,
              $pos / 1024,
              $pos / 1024 / 1024,
              $pos / 1024 / 1024 / 1024,
              ($pos - $last) / $interval / 1024 / 1024);
      $last = $pos;
    } while (sleep ($interval));

}

main (@ARGV);

# eof