# Code simplified for brevity (again)

my @files = get_files();
my $strings_file = shift(@ARGV) || "default";
my @init_strings;

foreach my $file (@files) {
  my @strings = @init_strings ||
                get_init_strings($strings_file, \@init_strings);
  push @strings, extra_strings();
  # manipulate files here
  ...
}

sub get_init_strings {
  my $file = shift;
  my $strings = shift;

  open FILE, $file or die "Couldn't open $file: $!\n";
  push @$strings, $_ while <FILE>;
  close FILE, $file or warn "Couldn't close $file: $!\n";

  return @$strings;
}