my $string = do{
  open my $fh, '<', 'filename' or die $!;
  local $/ = undef;
  <$fh>;
};

##</code><code>##

use File::Slurp;
my $text = read_file('filename');

##</code><code>##

use File::Slurp;
my @lines = read_file('filename');