#!/usr/bin/perl -w

use strict;

my @IDS;
my $last = [0,0,0,0,0]; # In case the first line has fields missing
while (<DATA>) {
    my @temp = split/\t+/; # allow multiple tab seperators.

    # set this element from the last if it's null
    $temp[$_] eq '' and $temp[$_] = $last->[$_] 
        for 0 .. $#temp;

    push @IDS, $last = \@temp; # push saving a reference
}

print "@{$_}" for @IDS;

=pod output

c:\test>219201
1234 5 20021201 1 0
5678 0 20021202 0 0
5678 0 0 0 10
9120 10 20021211 0 0
6543 5 20021202 0 0
6543 0 0 0 5
6543 0 0 0 5

=cut

__END__
1234	5	20021201	1	0
5678	0	20021202	0	0
	0	0		0	10
9120	10	20021211	0	0
6543	5	20021202	0	0
	0	0		0	5
	0	0		0	5