Hi everyone,

I have a file containing many GenBank records. I want to scan each of the GenBank record, if the record contains keywords, I want to print the accession number. I have looked at an example and tried to modify it as follows:

#!/usr/bin/perl 
use strict;
use warnings;
use BeginPerlBioinfo;

my $annotation;
my %fields;
my @genbank =();
my $locus = '';
my $accession = '';
my $reference = '';
my @features = ();
@genbank = get_file_data ('all_2.txt');

for my $line (@genbank){
    if($line =~/^LOCUS/){
         $line =~ s/^LOCUS\s*//;
         $locus = $line ;
         print $locus ;
   }elsif ($line =~/^ACCESSION/){
         $line =~ s/^ACCESSION\s*//;
         $accession = $line ;
    }elsif ($line =~/^REFERENCE/){
         $line =~ s/^REFERENCE\s*//m;
         $reference = $line;
         print $reference;
   }elsif ($line =~/^FEATURES/){
         %fields = parse_annotation($annotation);
         @features = parse_features($fields {'FEATURES'});
  foreach my $feature (@features) {
         my ($featurename) = ($feature =~ /^{5}(\S+)/);
         print $feature;
  if ($locus=~ /keywords/i) || ($reference=~ /keywords/i) || ($feature=~ /keywords/i){
     print $accession;
      }
    } 
  }
}

sub parse_features {
my ($features) =@_;
my (@features) = ();
while ($features =~/^{5}\S.*\n(^{21}\S.*\n)*/gm){
  my $feature = $&;
push (@features, $feature);
  }
return @features;
}
exit;

I can print locus and accession number, for the reference and feature part I can only print the first line. At the same time, I got the errors:

*Quantifier unexpected on zero-length expression in regex; marked by <-- HERE in m/ ^{5}(\S+)/< --HERE

Quantifier unexpected on zero-length expression in regex; marked by <-- HERE in/^{5}\S.\n(^{21}\S.\n)* <-- HERE**

I know it is something related with the regular expression but I do not know how to solve it as I am just the beginner. May I know how should I solve this so that I can print the whole part of reference and features instead of just the first line of them? Thanks.