I've used something like this before: 
use IO::File;
use strict;

my $tail = new IO::File;
$tail->open("<./log.dat");

while(1){
  my @lines=$tail->getlines();
  if(0==scalar(@lines)){
    # wait 1 second before trying again...
    # to keep from hogging CPU cycles
    sleep 1;
  }else{
    my $line;
    foreach $line(@lines){
      chomp $line;
      print "  \"$line\"\n";
    }
  }
}

[download]
I've originally wrote this code w/ a select/can_read but it ended up hogging the CPU so I put in the 1 second sleep.

A few problems with this code:

  1. Up to a 1 second delay between data being flushed to the log and the program detecting it
  2. Can't detect EOF, keeps waiting for more data even after the writing program has closed the logfile. Of course, tail -f has this same problem.
The program writing to the logfile needs to be flushing its output or you may get irregular results (i.e. sometimes partial lines, etc....).

In reply to Re: tee -f? by lhoward
in thread tee -f? by Jonathan

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