B::Deparse with the -p option can show you how Perl understands expressions. Unfortunately, the expression contains only constants, so it's evaluated at compile time, so the result isn't helpful:

$ perl -MO=Deparse,-p 1.pl
use strict;
my($test);
($test = (undef));
print("test = $test\n");
1.pl syntax OK
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You need to introduce variables to postpone the evaluation to runtime to get a more enlightening answer:

#! /usr/bin/perl
use warnings;
use strict;

my $test;
my $undef;
my $true = 1;
my $zero = 0;

$test = $true || ($undef && $undef != $zero) ? $undef : $zero;

print "test = $test\n";
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And, voilą:

use strict;
my($test);
my($undef);
(my $true = 1);
(my $zero = 0);
($test = (($true || ($undef && ($undef != $zero))) ? $undef : $zero));
print("test = $test\n");
1.pl syntax OK
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Nicely indented:

$test = (
    (
        $true || (
            $undef && (
                $undef != $zero
            )
        )
    ) ? $undef : $zero
)
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$true || ... returns 1, so the "then" part of the ternary is returned, i.e. $undef.

Maybe you wanted

$test = $true || ($undef && $undef != $zero ? $undef : $zero);
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($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
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