You could store the rest of the line (each sub-entry) in a separate array, then loop over that. Here's one I put together quickly:

while(<INPUT>){
  my (@prefix,@rest);
  chomp;
  (@prefix[0..2],@rest) = split /,/;
  for (@rest)
  {
    local $, = ',';
    local $\ = "\n";
    print @prefix,$_;
  }
}
[download]

A list of lists type structure would seem easiest for what you want do (like what you've done), although it would seem easier to create a hash keyed on a primary identifier (1401 in the example maybe). This would also let you give elements English names, which makes coming back to the file format later a lot easier. So maybe something like:

#!C:\Perl\bin\perl
use strict;
use warnings;

open my $input, "<", "input.csv" or die "Can not open: $!\n";
open my $output, ">", "output.csv" or die "Can not open: $!\n";

my %data = ();
while(<$input>){
  my @line = split /,/;
  
  my $key = shift @line;
  $data{$key} = {}; # Empty hash ref
  $data{$key}{store} = shift @line;
  $data{$key}{period} = shift @line;
  $data{$key}{dist} = \@line; # First three entries have been removed
}

foreach my $key (keys %data) {
  foreach my $dist ( @{ $data{$key}{dist} } ) {
    print $output join(",", $key, $data{$key}{store}, $data{$key}{peri
+od}, $dist), "\n";
  }
}

close $input;
close $output;
[download]

Please also take note that I have changed your open statements to 3-argument opens, swapped to lexical file handles and changed from the high precedence || to the low precedence or. The virtues of these structures have been extolled extensively in the archives.

This worked exactly as advertised. Thank you for your help.


TStanley
--------
People sleep peaceably in their beds at night only because rough men stand ready to do violence on their behalf. -- George Orwell

use warnings;
use strict;

use Text::xSV;
my $csv = Text::xSV->new(fh => *DATA, row_size_warning => undef);

while (my $row = $csv->get_row()) {
    my @prefix = splice @$row, 0, 3;
    foreach (@$row) {
        print join ',', @prefix, $_ . "\n";
    }
}

__DATA__
1401,PERISH STORE INV,Quarterly,(V) INV810 USER NAME (EDIT REPORT IF 0
+5309 PRSH INV),EXTRACT WAS RUN),(V) INV820 USER NAME (PERISHABLE INVE
+NTORY REPORT),(VTD8) D:\DEPT\ACCT\MAIL\INV820.DAT,(V) INV820C USER NA
+ME (PERISHABLE INVENTORY-BAKERY),(QUARTERLY RUN ONLY)
1402,PERSH INV BOOKS,Quarterly,(V) INV805 58 COPIES - USER NAME,(V) IN
+V805 2 COPIES - USER NAME,(V) INV805A XTRA COPIES-SAVE IN COMPUTER RO
+OM,ANNUAL STORE INVENTORY ONLY:,(V) INV805 58 COPIES - USER NAME,(V) 
+INV805 2 COPIES - USER NAME,(V) INV805A XTRA COPIES-SAVE IN COMPUTER 
+ROOM
1403,BAKERY INV BOOKS,Quarterly,(V) INV805 35 COPIES - USER NAME,(V) I
+NV805A 5 COPIES - SAVE IN COMPUTER ROOM,ANNUAL STORE INVENTORY ONLY:,
+(J) INV805 35 COPIES - USER NAME,(J) INV805A 5 COPIES - SAVE IN COMPU
+TER ROOM
1501,INV PRICE GUIDE,As Needed,(V) MSC052 BOTH COPIES ARE TO BE PUT IN
+ BINDERS AND,AND LEFT ON THE CABINETS BEHIND THE DP,SECRETARY'S DESK
[download]

$ perl tst.pl
1401,PERISH STORE INV,Quarterly,(V) INV810 USER NAME (EDIT REPORT IF 0
+5309 PRSH INV)
1401,PERISH STORE INV,Quarterly,EXTRACT WAS RUN)
1401,PERISH STORE INV,Quarterly,(V) INV820 USER NAME (PERISHABLE INVEN
+TORY REPORT)
1401,PERISH STORE INV,Quarterly,(VTD8) D:\DEPT\ACCT\MAIL\INV820.DAT
1401,PERISH STORE INV,Quarterly,(V) INV820C USER NAME (PERISHABLE INVE
+NTORY-BAKERY)
1401,PERISH STORE INV,Quarterly,(QUARTERLY RUN ONLY)
1402,PERSH INV BOOKS,Quarterly,(V) INV805 58 COPIES - USER NAME
1402,PERSH INV BOOKS,Quarterly,(V) INV805 2 COPIES - USER NAME
1402,PERSH INV BOOKS,Quarterly,(V) INV805A XTRA COPIES-SAVE IN COMPUTE
+R ROOM
1402,PERSH INV BOOKS,Quarterly,ANNUAL STORE INVENTORY ONLY:
1402,PERSH INV BOOKS,Quarterly,(V) INV805 58 COPIES - USER NAME
1402,PERSH INV BOOKS,Quarterly,(V) INV805 2 COPIES - USER NAME
1402,PERSH INV BOOKS,Quarterly,(V) INV805A XTRA COPIES-SAVE IN COMPUTE
+R ROOM
1403,BAKERY INV BOOKS,Quarterly,(V) INV805 35 COPIES - USER NAME
1403,BAKERY INV BOOKS,Quarterly,(V) INV805A 5 COPIES - SAVE IN COMPUTE
+R ROOM
1403,BAKERY INV BOOKS,Quarterly,ANNUAL STORE INVENTORY ONLY:
1403,BAKERY INV BOOKS,Quarterly,(J) INV805 35 COPIES - USER NAME
1403,BAKERY INV BOOKS,Quarterly,(J) INV805A 5 COPIES - SAVE IN COMPUTE
+R ROOM
1501,INV PRICE GUIDE,As Needed,(V) MSC052 BOTH COPIES ARE TO BE PUT IN
+ BINDERS AND
1501,INV PRICE GUIDE,As Needed,AND LEFT ON THE CABINETS BEHIND THE DP
1501,INV PRICE GUIDE,As Needed,SECRETARY'S DESK
[download]

In retrospect i.e. whilst watching my daughter learning to swim, it occurred to me that I probably ought to recommend the use of the print() &/or print_row() methods (of Text::xSV) to generate the output.

This is valid when there is no quoted fields with embeded commas:

while (<INPUT>) {
  chomp;
  my ($pref,$data) = (/^((?:[^,]*,){3})(.*)/);
  print OUTPUT "$pref$_\n" for split /,/, $data;
}
[download]