I liked your problem: If I understand your problem, the sequences in A must all be matched in order of appearance in B without repeating the sequence in A or in B. You may need to sequence through a possible 24 times, but I leave that up to you as you will see how to accomplish this. Try uncommenting the second data and you will see what I mean: My solution=)

#!/perl/bin/perl
use strict;

my @chem;
my %seqB;
my ($key, $value,$data, $pos, $x, $num, $seq);
my $DNA = "xxxxxxATGGAGyxxxTCGAzxxxxCGAATTTGAAxxwGAAT";
#my $DNA =  "CGATAAATGGAGTGACTCGAGATCGCGAATTTGCCAAACACGAAT";

while(<DATA>){
    chomp;
    @chem = split //;    
}
my $seq_prev ='';
for(1..10){

$num = @chem;
$num--;
for (0..$num){
$key = join '', @chem[0..$_];
if($DNA =~ /($key)/i){ $seq = $`; $data = $key; $pos=$_+1; }
#first sequence in A found
}

#remove the matched squence from future possible matches
splice @chem, 0, $pos;

#show the results
my $chem= join '', @chem;
print "FIRST SEQ MATCH FOUND: $seq_prev|< $data >|$chem\n";
print "\nDNA(B)- BEFORE < $data >: $seq";
$seq_prev = $data.$seq_prev;
$seqB{$data} = $seq;
#remove the matched DNA B pattern matched data
$DNA =~ s/$seq$data//;

# exit(0) if $DNA eq '';  #if you wanted to match more than 4
}

print "AS A HASH TABLE KEY:VALUE PAIRS\n";
foreach (keys %seqB){
    print "$_ = $seqB{$_}\n";
}
__DATA__
ATGGAGTCGACGAATTTGAAGAAT
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It gives you what you want for both the data you provided and for any generic data sets. JamesNC :0)