Hi baxy! I did as you suggested in the update, the script run, but the output was empty! I run: 
use strict;
use warnings;
my $infile = "rep_set_ass_tax.fna";
my $outfile = "seq_id.txt";

open(IN, ">>", "rep_set_ass_tax.fna") or die "Died!!"; 

 while (my $line=<IN>) { 
   if($line=~/>(\d+)/) {
     print $1 . "\n";
   } 
 }

[download]
What's the problem? 
 close IN;

[download]

In reply to Re^2: writing array element to a file by francesca1987
in thread writing array element to a file by francesca1987

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