Perl Tail ?

[perlAffen]

Hi, In windows I am using a nice piece of perl code to tail a log file. It does a nice job until the file becomes very large, ie over 20 meg, then the perl process starts to be a memory hog. I tried using a cygwin tail, but it locks the file so the original process can't write to it. This perl code does NOT lock the file. Can someone suggest how I might grab new chunks of a large file efficiently ? The current code is like this

while(-s $file ) {
  open(TF,$file) || last ;
  seek(TF,$curpos,0);
  @lines=<TF>;
  $cursorposition = tell(TF);
  last if ((stat(_))[7] < $cursorposition);
    foreach $nline (@lines){
    $newline = substr $nline, 24;
    # write out to tailfile    $newline
    }    
  close(TF);
  sleep 1;
}
}
else
    { sleep 5; }
}

Thanks

[marto]

Hi,

Further to the above there is also File::Tail.

Hope this helps.

Martin

[ikegami]

tail can efficiently be done using File::ReadBackwards.

# Displays the last $n lines of $file_name,
# earliest first.

my $file_name = 'file.log';
my $n = 5;

my $fh = File::ReadBackwards->new($file_name)
   or die("Can't read input file: $!\n");

my @lines;
for (1..$n) {
   my $line = $fh->readline();
   last if not defined $line;
   unshift(@lines, $line);
}

print foreach @lines;

Update: marto's suggestion seems to be more appropriate.

[rinceWind]

A super search on tail will give examples of how to do this, including my post Re: Log file tailing.

[LanceDeeply]

i tried Perl Power Tools v0.14: tail and it seems to work ok in windows. i havent tried it on a 20 meg file though...

hth

[Skeeve]

Is there any need for you to read in the whole file?

@lines=<TF>;

Why not simply read line by line and don't store them?

[perlAffen]

So this is an efficient way to do the Unix equivalent ?

tail -f logfile > tailfile

I would like to tail it for 10 minutes, restart the tail process for another 10 mintues, copying off tailfile to tailfile.chunk before writing to tailfile again. COuld I use this to do it ? I will check tail archives too.

[QM]

I recall many years ago that unix tail is broken on large files, such that I wrote my own Perl tail for one job. You might want to look at tail for Perl Power Tools.

I would like to tail it for 10 minutes, restart the tail process for another 10 mintues, copying off tailfile to tailfile.chunk before writing to tailfile again

Please be more specific. Are you intending to skip (lose) 10 minutes of logfile? Do you just want to split the logfile into chunks at 10 minute intervals?

What is the fundamental problem you're trying to solve?

[graff]

I tried using a cygwin tail, but it locks the file so the original process can't write to it.

LOL -- that's the best joke I've seen about MS Windows in a while. I suppose it could just be taken as a (yet another?) case of midguided implementation on the part of cygwin, but based on the whole brain-damaged approach to file locking foisted by MS, cygwin should not take all the blame (or should at least admit only to justifiable failure).