use strict;
use warnings;

package PushableFH;

use strict;
use warnings;

sub TIEHANDLE {
	my $class = shift;
	my $rfh = shift;
	my $obj = {};
	$obj->{FH} = $rfh;
	$obj->{PUSHED} = [];
	bless $obj, $class;
}

sub READLINE {
	my $self = shift;
	my $fh = $self->{FH};
	return ( @{$self->{PUSHED}} > 0 ) ? pop @{$self->{PUSHED}} : <$fh>;
}

sub push_fh {
	my $self = shift;
	push @{$self->{PUSHED}}, @_;
}

package main;

use strict;
use warnings;
use vars qw/*FILEHANDLE/;

my $fhobj = tie *FILEHANDLE, "PushableFH", \*DATA;

my $line = <FILEHANDLE>;    # Read the first line from the filehandle.
print $line;

$fhobj->push_fh("Hello world!\n");  # Push something onto the FH.

$line = <FILEHANDLE>;  # Read what was just pushed.
print $line;

$line = <FILEHANDLE>;  # Read the next physical line from FH.
print $line;

__DATA__
This is the first line.
This is the second line.