#! perl -lsw
use strict;

my @reps = map{ sprintf '%05d', $_ } 0 .. 20;
while(<DATA>) {
	my $n=0;
       # redundant /e option  removed 
       # per [Abigail-II]'s comment below.
	s/\d{5}/$reps[$n++]/g;   
	print;
}
__DATA__
00000000000000000000000000000000000000000000000000000000000000000000000000000000000000
00000xxxx00000xxxxx00000xxxx00000xxxxx00000xxx00000xxx00000xx00000xxx00000x00000x00000

##</code><code>##

c:\test>234342
00000000010000200003000040000500006000070000800009000100001100012000130001400015000160

00000xxxx00001xxxxx00002xxxx00003xxxxx00004xxx00005xxx00006xx00007xxx00008x00009x00010