File::Tail::FAM - Tail using the File Alteration Monitor (FAM)


    use File::Tail::FAM;

    my $tail = File::Tail::FAM->new(
        file => "/tmp/abc"

       # Blocking read (without wasting any CPU time)
    while(defined( my $data = $tail->read() )) {
        print "This just got added: [$data]\n";

       # Or, read data in non-blocking mode
    my $data = $tail->read_nonblock();
    if(defined $data) {
        print "This just got added: [$data]\n";
    } else {
        print "Nothing happened\n";


File::Tail::FAM reports when new data chunks are appended to a given file. Similar to the Unix command

    $ tail -f filename

it watches a file grow continuously and reports whenever a new chunk of data has been added.

Differently from the traditional approach of periodically polling the file (used by tail -f and File::Tail), File::Tail::FAM uses the File Alteration Monitor to get notified by the Linux kernel whenever new data gets added to the watched file.

This way, File::Tail::FAM will simply block (and therefore won't use any CPU cycles) until the kernel's notification mechanism wakes it up when new data has arrived.

File::Tail::FAM uses the Perl module SGI::FAM, which provides an API to the File Alteration Monitor (FAM) library routines which come with many Linux distributions (man 3 fam) and are available for download at


Copyright 2005 by Mike Schilli, all rights reserved. This program is free software, you can redistribute it and/or modify it under the same terms as Perl itself.


2005, Mike Schilli <>