@t = split(/\t/, $_) ;
  $t[4]= $AB{[4]} ;

##</code><code>##

  $AB{$alpha_numeric_field} = $numeric_field ;

##</code><code>##

  if ($var1[2] and exists $Ab{$var1[2]}) {
    print OUT "$var1[0]\t$var1[1]\t$var1[2]\t$AB[4]\n" ;
  }

##</code><code>##

  @var1 = split(/\t/,$_) ;

##</code><code>##

  ($field_name, $other_field, $further_field, ...) = split(...) ;