Programmatically read from STDIN or input file in Perl

Question

What is the slickest way to programatically read from stdin or an input file (if provided) in Perl?

Answer 1

if(my $file = shift) { # if file is specified, read from that
  open(my $fh, '<', $file) or die($!);
  while(my $line = <$fh>) {
    print $line;
  }
}
else { # otherwise, read from STDIN
  print while(<>);
}