for (@b){$a[1]=$_;say:}

##</code><code>##

my @a=();
foreach $a[0](`cat file`){
 foreach $a[1](@b){
  foreach $a[2](grep (/4/, @c)){
   <More statements>
}}}

##</code><code>##

my @a=();
foreach (`cat file`){
 $a[0]=$_;
 foreach $a[1](@b){
  $a[1]$_;
  foreach $a[2](grep (/4/, @c)){
   $a[2]=$_
   <More statements>
}}}