THe following sample code should do it for you. You should omit the updateFile related code - that's just there to get the test file updated.

use strict;
use warnings;

my $logFileName = 'test.txt';
my $lastPos = 0;
my $endTime = time + 60;

while (time < $endTime)
  {
  next if ! -e $logFileName;
  next if $lastPos >= -s $logFileName;
  
  open inFile, '<', $logFileName;
  seek inFile, $lastPos, 0;
  print while <inFile>;
  $lastPos = tell inFile;
  close inFile;
  }
  continue
  {
  sleep (5);
  updateFile ();
  }

sub updateFile
{
open outFile, '>>', $logFileName;
print outFile 'Line added to file at ' . (join ', ', localtime) . "\n"
+;
close outFile;
}
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Printed:

Line added to file at 30, 16, 12, 30, 10, 105, 3, 333, 1
Line added to file at 35, 16, 12, 30, 10, 105, 3, 333, 1
Line added to file at 40, 16, 12, 30, 10, 105, 3, 333, 1
Line added to file at 45, 16, 12, 30, 10, 105, 3, 333, 1
Line added to file at 50, 16, 12, 30, 10, 105, 3, 333, 1
Line added to file at 55, 16, 12, 30, 10, 105, 3, 333, 1
Line added to file at 0, 17, 12, 30, 10, 105, 3, 333, 1
Line added to file at 5, 17, 12, 30, 10, 105, 3, 333, 1
Line added to file at 10, 17, 12, 30, 10, 105, 3, 333, 1
Line added to file at 15, 17, 12, 30, 10, 105, 3, 333, 1
Line added to file at 20, 17, 12, 30, 10, 105, 3, 333, 1
[download]