unless.pl

gistfile1.txt

mhorsfall@tworivers:~$ cat unless.pl 
use strict;
use warnings;

my @strs = (
  '$x = do { unless ("cat" eq "cat") { } };',
  '$x = do { unless ("cat" ne "cat") { } };',
  '$x = do { if ("cat" eq "cat")     { } };',
  '$x = do { if ("cat" ne "cat")     { } };',
);

for my $str (@strs) {
  my $x;
  eval $str; die "Failed $@\n" if $@;
  $x ||= 0;

  print "$str: $x\n";
}

mhorsfall@tworivers:~$ perl unless.pl 
$x = do { unless ("cat" eq "cat") { } };: 1
$x = do { unless ("cat" ne "cat") { } };: 0
$x = do { if ("cat" eq "cat")     { } };: 0
$x = do { if ("cat" ne "cat")     { } };: 0