UNIX for Dummies Questions & Answers

Very simple problem I am not able to solve. I have been trying to modify the following code:

Code:

awk '{t=$1; c = x}{for (i = 1; i <= length; i += wn)print t FS"" substr($2, i, mx) > ("block" ++c)}' mx=100 wn=100 infile.txt

What I am tryng to acccomplish, I have a bunch of files where the first number at the top is the number of sequences followed by the length of the sequences. Then, the first column is the SequenceID followed by the actual sequence, something like this:
I need to grab the first, let say 20 characters and create a file named block1.txt something like this:
Now the second number in the top is = 20 which corresponds to the length of the sequences. Then, I need to 'slide' the window let say 10 characters and grab the following 20 characters and create a second file named block2.fas, so on and so forth.
I am attaching a little example of the input file and the first 2 output (block) files.
Thanks a lot!

So what's wrong with the code?

Get 20 characters with 10 characters back slide (same as your sample output)

Code:

awk '{t=$1; c = x}{for (i = 1; i <= length; i += wn)print t FS"" substr($2, i, mx) > ("block" ++c)}' mx=20 wn=10 infile.txt

Get the output as the attach files (block1.txt, block2.txt, etc)

Code:

awk '{t=$1; c = x}{for (i = 1; i <= length; i += wn)print t FS"" substr($2, i, mx) > ("block" ++c)}' mx=50 wn=10 infile.txt

I need to include at the very top of each output (block?) file the number of sequences (12 in this particular case) followed by the length of the sequences (in my example 20).
I just do not know how to do it!
I will be very thankful if someone can help me with this problem!
Thanks in advance!

first awk for title.

Code:

awk 'NR==1{s=$1}{l=length($2)>l?length($2):l}END {for (i = 1; i <= l; i += wn) print s FS mx > ("block" ++c)}'  mx=50 wn=10 infile.txt

awk 'NR>1 {t=$1;c = x; for (i = 1; i <= length($2); i += wn)print t FS"" substr($2, i, mx) >> ("block" ++c)}' mx=50 wn=10 infile.txt