-s, --sleep-interval=S
  with -f, sleep for approximately S seconds (default 1.0) between iterations

##</code><code>##

# generate test log file in bash
$ while true ; do echo $(( ++i )) ; sleep .1 ; done > test

##</code><code>##

# little File::Tail demo
use Time::HiRes qw( gettimeofday );
use File::Tail;

$| = 1;

my $tail = File::Tail->new( name => './test', maxinterval => 0.1 );

my $usec;
my $sec_since_epoch;
my $line;

while ( defined( $line = $tail->read() ) ) {
  ( $sec_since_epoch, $usec ) = gettimeofday();
  printf "%d.%d\n", $sec_since_epoch, $usec;
}