Hi Random Walk,
Thanks so much answering. I've tested your code. It works great.
Just wonder how can I modify the code, such that it capture the file automatically.

Currently I have to pass the all files argument manually like this:

perl mycode.pl data1P.fa data1R.fa data2P.fa data2R.fa ....etc
[download]

Because there are many many files like this. Can it be automated?