while ( <INFILE> ) {
    chomp;
    s/^\s+//g;
    my ($first, $second) = split;
    # now if first 'column' was blank then the second will be 
    # in $first and $second will be undef so just swap them
    ($first, $second) = ($second, $first) unless $second;
    push @first, $first;
    push @second, $second;    
}