The following is a parallel demonstration when extra performance is desired for very large sequences. Otherwise, the serial demonstration is faster.

use strict;
use warnings;

use BioUtil::Seq;
use constant { HDR => 0, SEQ => 1 };

use MCE::Flow;
use MCE::Shared;

mce_open my $out_fh, '>', \*STDOUT or die "open error: $!\n";

# From the documentation:
#
# FastaReader returns an anonymous subroutine, when called, returns
# a fasta record which is a reference of an array containing the fasta
# header and sequence. By default, spaces and \r?\n are trimmed from
# the sequence.
#

mce_flow {
   max_workers => 4,
   chunk_size  => 1,
   input_data  => FastaReader("input_file.fasta")
},
sub {
   my ( $mce, $chunk_ref, $chunk_id ) = @_;
   my $fa = $chunk_ref->[0];

   # my $fa = $_;  # same thing for chunk_size => 1
   # therefore, the 2 lines above may be omitted

   # print ">$fa->[HDR]\n$fa->[SEQ]\n";

   my $name = ( split(/ /, $fa->[HDR], 2) )[0];
   my $output;

   while ( $fa->[SEQ] =~ /(?<=(.....))abc(.{10})def(?=(.....))/g ) {
      $output .= "$name: $1, $2, $3\n";
   }

   print $out_fh $output if length($output);
};
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Regards, Mario.