Hi to neilfws & all others Thanks for the response. I made-up the code, please correct it. Can you people suggest me tutorial links or textbooks for Bioperl.

#!/usr/bin/perl -w
use strict;

use Bio::SeqIO;

my $seqin  = Bio::SeqIO->new(-file => "euplotes.txt",      -format => "fasta");

my $seqout = Bio::SeqIO->new(-file => ">outfile.txt", -format => "fasta");

while(my $seq = $seqin->next_seq) 


 {
  if($seq->desc) =~/^FULL-LENGTH\s+/ {

    $seqout->write_seq($seq);
  }
}