#!/usr/bin/perl
use strict;
use warnings;

while (<>) {
	my $datapos = tell DATA;
	while (<DATA>) {
		print;
	}
	seek DATA, $datapos, 0;
}

__DATA__
foo
bar
baz
Your data here!
Add, remove, or change lines while running the program.
Every time you hit Return, you will see the current contents of DATA.