#!/usr/bin/perl -w
use strict;

use Fatal qw(open close); # so I don't have to bother testing them

my @files= @ARGV;
my %marker= map { $_ => 0 } @files;

while( keys %marker)
  { foreach my $file (@files)
      { if( exists $marker{$file})
          { open( my $fh, '<', $file);
            seek( $fh, $marker{$file}, 0); # the 0 means 'set the new position in bytes to' $marker{$file}
            if( defined( my $line=<$fh>))
              { print $line;
                $marker{$file}= tell $fh;
              }
            else
              { delete $marker{$file}; }
            close $fh;
          }
      }
  }