>sequence1_name
ATGACTGTTGG...etc.
generally some fixed number of letters per line

##</code><code>##

my $seq_name;
my %seqs_hash;
while (my $line = <SEQS>) {
  chomp $line;
  if ($line =~ m/\>\s*(.+)$/) {
    $seq_name = $1;
  } else {
    $line =~ s/\s//g;
    $seqs_hash{$seq_name} .= $line;
  }
}

##</code><code>##

my $seq_name;
my %seqs_hash;
my %temp_hash;
while (my $line = <SEQS>) {
  chomp $line;
  if ($line =~ m/\>\s*(.+)$/) {
    $seq_name = $1;
  } else {
    $line =~ s/\s//g;
    push(@{$temp_hash{$seq_name}}, $line);
  }
}

foreach my $key (keys %temp_hash) {
  $seqs_hash{$key} = join("", @{$temp_hash{$key}});
}