Cool/useful short examples of Perl?

[David Matthewman]

On 8 Jun 2011, at 13:41, Paul Makepeace wrote:

> On Wed, Jun 8, 2011 at 13:17, Tom Hukins <tom at eborcom.com> wrote:
>> On Wed, Jun 08, 2011 at 02:00:41PM +0200, Abigail wrote:
>>> I'd rather go for sacking people that don't know the difference
>>> between
>>> 
>>>     if (something) { ... }
>>> 
>>> and
>>> 
>>>     unless (!something) { ... }
>> 
>> It's sunny outside and pubs are open:  I can think of worse times to
>> lose my job.
>> 
>>> Or does everyone think they are always equivalent?
>> 
>> I'm not everyone, and with a language as flexible as Perl I hesitate
>> to make strong statements involving words like "always", but I don't
>> recall encountering a situation where they differ.
> 
> $ perl -le 'print "$_ == !!$_ ? ", $_ == !!$_ ? "yes" : "no" for (-1,
> 0, 1, 2, undef)'
> -1 == !!-1 ? no
> 0 == !!0 ? yes
> 1 == !!1 ? yes
> 2 == !!2 ? no
> == !! ? yes

Well, -1 may not equal !!-1, but truthwise it's the same, so it's the same to an if or unless statement.

I realise this is getting a bit silly, but:


foreach my $test_item (-1, 0, 1, 2, undef, '') {
    print "$test_item:\t" 
        . return_truth_by_if_not($test_item) . ', '
        . return_truth_by_unless($test_item) . ', '
        . return_truth_by_if_not(!$test_item) . ', '
        . return_truth_by_unless(!$test_item) . ', '
        . return_truth_by_if_not(!!$test_item) . ', '
        . return_truth_by_unless(!!$test_item) . "\n";
}

sub return_truth_by_if_not {
  my $value = shift;
  if (!$value) {
      return 'non';
  }
  else {
      return 'oui';
  }
}

sub return_truth_by_unless {
  my $value = shift;
  unless ($value) {
      return 'non';
  }
  else {
      return 'oui';
  }
}

-- 
David Matthewman