my $s1='TCGAGTGGCCATGAACGTGCCAATTG';
my $s2='ATGATCCTG';
($s1,$s2) = ($s2,$s1) if length($s1) > length($s2);
my $len= length $s1;
print "Matches:\n";
for (my $i=0; $i+$len+10 <= length $s2; ++$i) {
    print substr($s2, $i, $len+10),"\n";
}

##</code><code>##

Matches:
TCGAGTGGCCATGAACGTG
CGAGTGGCCATGAACGTGC
GAGTGGCCATGAACGTGCC
AGTGGCCATGAACGTGCCA
GTGGCCATGAACGTGCCAA
TGGCCATGAACGTGCCAAT
GGCCATGAACGTGCCAATT
GCCATGAACGTGCCAATTG