#!/usr/bin/perl -w

use strict;
use Bio::SeqIO;

my @files   = <*.seq>;
my $pattern = '[AN]{10}';

foreach my $file (@files) {
   my $seqio = Bio::SeqIO->new( -file => $file );
   while ( my $seqobj = $seqio->next_seq() ) {
      my $raw_seq = $seqobj->seq();
      if ( $raw_seq =~ /$pattern/o ) {
         print "Found a polyA tail in $file.\n";
      }
   }
}

##</code><code>##

Found a polyA tail in myfile
Found a polyA tail in myfile