Re: order of operations with conditionals at the end

As a general solution to determining the order of operations, you can add the -p option to -MO=Deparse; you write it like -MO=Deparse,-p. This adds parentheses showing how perl parses your code.

ken@ganymede: ~/tmp
$ perl -Mstrict -Mwarnings -MO=Deparse,-p -E '
> my $message = "Congrats" unless not defined $reward;
> '
Global symbol "$reward" requires explicit package name at -e line 2.
-e had compilation errors.
use warnings;
use strict 'refs';
BEGIN {
    $^H{'feature_unicode'} = q(1);
    $^H{'feature_say'} = q(1);
    $^H{'feature_state'} = q(1);
    $^H{'feature_switch'} = q(1);
}
((not defined(${'reward'})) or (my $message = 'Congrats'));
ken@ganymede: ~/tmp
$
[download]

You'll see how you get an error about $message not being declared: this is different from not being defined. Here it is again with this variable being declared but left undefined.

ken@ganymede: ~/tmp
$ perl -Mstrict -Mwarnings -MO=Deparse,-p -E '
> my $reward;
> my $message = "Congrats" unless not defined $reward;
> '
use warnings;
use strict 'refs';
BEGIN {
    $^H{'feature_unicode'} = q(1);
    $^H{'feature_say'} = q(1);
    $^H{'feature_state'} = q(1);
    $^H{'feature_switch'} = q(1);
}
my($reward);
(defined($reward) and (my $message = 'Congrats'));
-e syntax OK
ken@ganymede: ~/tmp
$
[download]

Note differences between the error and error-free versions:

((not defined(${'reward'})) or (my $message = 'Congrats'));
(defined($reward) and (my $message = 'Congrats'));