my $last4 = '';
my $buffer = '';
my $find = '1234';
my $find_re = qr /$find/;
my $length = length $find;
my $chunk = 7;  # 2**20 or some such is more logical!
my $pos = 0;
while ( my $read_length = read ( DATA, $buffer, $chunk ) ) {
    $buffer = $last4 . $buffer;
    print "got last-$last4\tbuffer-$buffer\n";
    while ($buffer =~ m/$find_re/g) {
         print "match at ", $pos - (length $last4) -$length  + pos $buffer, "\n";
    }
    $last4 = substr $buffer, -$length, $length, '';
    $last4 = '' if $last4 =~ m/$find_re/;  # stop double match bug
    $pos += $read_length;
}
__DATA__
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