package Tie::File::Custom;
use strict;
use warnings;
use Carp;

sub TIEHANDLE {
    my ($class, $file) = @_;
    my $self = {};
    bless $self, $class;
    open ($self->{FH}, '<', $file) or croak "Error opening file : $!";
    $self->$_() for qw(LINES BUFF NL);
    return $self;
}

sub READLINE {
    my $self = shift;
    my $fh = $self->{FH};
    my $lines;

    # We already have data in our window 
    if ( $self->{WINDOW} ) {
        $lines = $self->{WINDOW} =~ s/($self->{NL})/$1/gs;
        if ( $lines >= $self->{LINES} ) {
            (my $data, $self->{WINDOW}) = $self->SPLIT();
            return $data;
        }
        # The window isn't a complete line but we are out of file
        return delete $self->{WINDOW} if eof $fh;
    }

    # We don't have anything and we can't get anything
    return undef if eof $fh && ! $self->{WINDOW};

    # We need to get more into our window 
    local $/ = \$self->{BUFF};
    while ( ! eof $fh ) {
        $self->{WINDOW} .= <$fh>;
        $lines = $self->{WINDOW} =~ s/($self->{NL})/$1/gs;
        last if $lines >= $self->{LINES}
    }

    # We need to check if we got here because we have enough lines or 
+ran out of file
    if ( $lines >= $self->{LINES} ) {
        (my $data, $self->{WINDOW}) = $self->SPLIT();
        return $data;

    }
    return delete $self->{WINDOW};
}

# We really should be more efficient about this
# We should also have lots of tests to fix edge cases
sub SPLIT {
    my $self = shift;
    my @part = split /($self->{NL})/, $self->{WINDOW};
    my $data = join '', @part[ 0 .. ( $self->{LINES} * 2 ) - 1 ];
    my $rest = join '', @part[ $self->{LINES} * 2 .. $#part ];
    return ($data, $rest);
}

sub LINES { $_[0]->{LINES} = $_[1] || $_[0]->{LINES} ||    1; $_[0]->{
+LINES} }
sub BUFF  { $_[0]->{BUFF}  = $_[1] || $_[0]->{BUFF}  || 8192; $_[0]->{
+BUFF}  }
sub NL    { $_[0]->{NL}    = $_[1] || $_[0]->{NL}    || "\n"; $_[0]->{
+NL}    }
sub CHOMP { $_[1] =~ s/$_[0]->{NL}$// }

"This Statement is false";
[download]

#!/usr/bin/perl
use strict;
use warnings;
use Tie::File::Custom;

tie *fh, 'Tie::File::Custom', 'file.txt' or die "Unable to tie : $!";

(tied *fh)->LINES( 2  ); # Return 2 lines at a time
(tied *fh)->BUFF( 100 ); # Read 100 bytes at a time since we expect sh
+ort lines

while ( <fh> ) {
    print $_, "-\n";
}
[download]

#!/usr/bin/perl
use strict;
use warnings;
use Tie::File::Custom;

tie *fh, 'Tie::File::Custom', 'num.dat' or die "Unable to tie : $!";
(tied *fh)->NL( "\n\\d+\n" ); # Lines with numbers by themselves are r
+ecord terminators

while ( <fh> ) {
    (tied *fh)->CHOMP( $_ );
    print "$_\n";
}
[download]