#/usr/bin/perl

$file = "my-log_file.log";

$o = tie @array, 'Tie::File', $file;

$o->flock; # lock the file. See Note 1.
$line_count = 0;

while( 1 ){
  
  if( $line_count < $#array ){ #New line is added
    $line_count++;
    foreach $line($line_count .. $#array )
    {

    #### Your code to parse @array[$line];####

    }
    $line_count = $#array;  
  }
  sleep(1); #parse every second
}