Salutations to the esteemed Monks here,
my problem is as follows:
Following is what my program looks like:

print "Enter the filename of file having codon data:\n";
$file = <STDIN>;
chomp ($file);
open (IN, $file) or die "Error opening $file: $!\n";
print "\n\n";

while ($seq = <IN>)
{
 print "$seq\n";
 @triplets = unpack ("a3" x (length($seq)/3, $seq);
 print "@triplets\n\n";
}
print "\n\n";

[download]

Now, suppose if the text file "codons" (no quotes) contains the following:

atgcatccctttaat
tctgtctga

[download]

Then the output of my program is something like this:

atgcatccctttaat

atg cat ccc ttt aat

tctgtctga
tct gtc tga

[download]

Note that i am splitting a sequence into array elements, where each element of the array corresponds to three characters of the sequence and i am doing this without using any delimiter like , or : (so i can't use split).

My problem is that the unpack function is highly mysterious to me. The "x" for example is the cross operator i believe but i don't know what it does. The "a3" inside the parenthesis within unpack is compulsory it turns out; replace "a3" with "b3" and u get something weird as output. So could someone please shed some light on the unpack function and explain how it is operating here, in my program.

20050301 Janitored by Corion: Added formatting

In reply to splitting a sequence using unpack by Rashmun

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