$/ = 'XXFFDDF';               # set the input record separator
my $base = 'filename';
my $i = 0;
while (<>) {                  # read one section at a time
  my $filename = "$base$i";   # generate a new filename
  open(OUT, ">$filename")     # create and write a new file
    or die "Can't open $filename: $!\n";
  print OUT;
  $i++;
}
[download]

You can generate the filenames however you prefer. I just chose a very simple way of generating the names as an example.

If each section is very long, you might want to read the file in in smaller chunks to conserve memory.

One final note: this puts the XXFFDDF at the end of each file. If you want to put it at the beginning, the code will need to be somewhat different.

local $/ = "XXFFDDF";   # delimiter

while (<INPUT>) {
   open(OUTPUT, "> output.$.")   # output.1, output.2, etc
      or die "output.$.: $!";   
   print OUTPUT;
   close(OUTPUT);
}
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#! /usr/bin/perl -w

my $infil = $0;
my $separator = "XXFFDDF";
local $/ = $separator;

sysopen(INFIL,$infil,O_RDONLY) || die "Can't open $infil: $!.\n";
while(<INFIL>){
  my $out_file = "$infil.$.";
#  s/$separator//;
### if you want to remove your file separator also, uncomment above li
+ne .....
   sysopen(OUT,$file,O_RDWR|O_CREAT|O_EXCL) || die "Can't open for wri
+te tst.$.: $!.\n";
  print OUT $_;
}
close(INFIL);
[download]

This code would work fine but has the disadvantage of storing an entire file of data in $_. While the file you are splitting would not be likely to have huge sections between the $seperator's you might never know if the code could be used in a situation where we are placing large amounts of data into memory.

my $fil_count = 0;
my $delim = 'XXFFDDF';
open IN, 'in.txt' or die "Can't open in.txt: $!\n";
open OUT, '> out0.txt' or die "Can't write to out0.txt: $!\n";
while (<IN>)
{
  if (/^(.*?)$delim(.*)$/) {
    print OUT $1 if $1;
    close OUT;
    $fil_count++;
    open OUT, '> out' . $fil_count . '.txt' or die "Can't write to out
+${fil_count}.txt: $!\n";
    print OUT $2 if $2;
  }
  else {
    print OUT $_;
  }
}
close IN;
[download]

If you can stand putting the entire line with the delimiter in the new file, there's a quick and dirty version for this:

perl -pe 'BEGIN { $x = "aaa000"; } open STDOUT, ">".(++$x) if /XXFFDDF
+/' <input >initial_output
[download]

-- Randal L. Schwartz, Perl hacker

use strict;
local $/ = undef; # grab everything from file

open FILE, "my_file" or die $!;
foreach $data_block (split /match_instance/, <FILE>) {
    open OUTPUT, "new_file_name" or next;
    print OUTPUT $data_block;
    close OUTPUT;
}
[download]