how to open a file,match some data from it,extract the data which matched and save/write it to another file?
for example in a fasta fomat DNA dequence,I want to remove all the header lines and store them to a separate file.

Well .... this is the sort of thing you can do ....

Code:

open (FH,"requests.xyz") or die; open (FHO,">pythoners.xyz") or die; while (<FH>) {        /Python/ and print FHO;        }

... but I am concerned that you'll really need to learn a lot more basics to tailor this to do what you need.   I can recommend either this or a good book, but learning all of Perl via a question and answer session isn't very practical.

I recommend anyone working with DNA stuff checks out bioperl:

www.bioperl.org

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