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;
}