How does it not work? Are you sure you want to declare the variable inside the eval rather than declaring it outside and then merely set it inside?

Also, what makes you think that eval is shorter or simpler than the first code snippet? You're free to use the A?B:C in the first snippet too.

O'Reilly's Advanced Perl Programming sais that eval'ed code is executed in the environment of the surrounding code, just as if the eval wasn't there - so declaring it inside or outside of the eval block is irrelevant
Anyway, the eval just added noise to the core of my post, that's why I removed it from the follow up example.

That does not change the scoping rules , {   } introduces a new scope

$ perl -le " eval { my $foo = 1; } ; print $foo; "


$ perl -le " use strict; eval { my $foo = 1; } ; print $foo; "
Global symbol "$foo" requires explicit package name at -e line 1.
Execution of -e aborted due to compilation errors.
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• Look at the scope of your my $ref variable.

  $ perl -e 'my $foo = "bar"; eval { my $foo = "biz" }; print $foo'
  bar
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• Is there a chance for anything inside of the eval block to die / throw an exception? If not, $@ will never be set. See die and perlvar.

Firstly, I concur with comments above regarding scope and a lack of error description or output.

My immediate thought was that you really want:

my $ref = eval { defined($asset->{related_files}) ? decode_json($asset
+->{related_files}) : []; };
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If the eval is failing, print out why, e.g. say $@ if $@; or something similar. Printing "error" is as useless as telling us "it didn't work".

Decide whether your condition should test for truth, defined-ness or existence. See the first three example lines from exists:

    print "Exists\n"    if exists $hash{$key};
    print "Defined\n"   if defined $hash{$key};
    print "True\n"      if $hash{$key};
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Try a much simpler form of the two constructs. Maybe something like:

$ perl -Mstrict -Mwarnings -E 'my $x; eval { my $y = defined $x ? 1 : 
+0; }; say $@ if $@; say $y;'
Global symbol "$y" requires explicit package name at -e line 1.
Execution of -e aborted due to compilation errors.

$ perl -Mstrict -Mwarnings -E 'my $x; my $y = eval { defined $x ? 1 : 
+0; }; say $@ if $@; say $y;'
0
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Although I can't see it being an issue here, autovivification could be a factor in this type of code and should at least be considered.

If you still haven't tracked down the problem by this stage, now would be the time to start looking at SQL and JSON.

#! perl

use Data::Dumper;
use JSON::XS;

my $asset = {
        ## rename this var to something else to test the 'undefined' c
+ase
        related_files => '{
     "firstName": "John",
     "lastName" : "Smith",
     "age"      : 25,
     "address"  :
     {
         "streetAddress": "21 2nd Street",
         "city"         : "New York",
         "state"        : "NY",
         "postalCode"   : "10021"
     },
     "phoneNumber":
     [
         {
           "type"  : "home",
           "number": "212 555-1234"
         },
         {
           "type"  : "fax",
           "number": "646 555-4567"
         }
     ]
 }'
};



my $ref;
if($asset->{related_files}){
 $ref = decode_json($asset->{related_files});
}else{
 $ref = [];
}

print Dumper($ref);

## simpler shorthand-code doesn't work, why?
my $ref = $asset->{related_files} ? decode_json($asset->{related_files
+}) : [];

print Dumper($ref);
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Really? Your script works as expected on this machine. I suppose you might have a severely broken JSON::XS - that's the only place I can see it possibly breaking. Tried JSON::PP?

perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'

Here is a demonstration of it working, and some alternatives :)

#!/usr/bin/perl --
use strict; use warnings;
use Data::Dump;
use JSON::XS;

my $ref = { foo => q{[1,2,3]} };
for my $key( qw/ bar foo /) {
    {
        my $foo;
        if( $ref->{$key} ){
            $foo = decode_json( $ref->{$key} );
        } else {
            $foo = [];
        }
        dd $foo;
    }

    {
        my $foo = [];
        if( $ref->{$key} ){
            $foo = decode_json( $ref->{$key} );
        }
        dd $foo;
    }

    {
        my $foo = $ref->{$key}
                  ? decode_json( $ref->{$key} )
                  : [];
        dd $foo;
    }

    {
        my $foo = eval { decode_json( $ref->{$key} ) } || [];
        dd $foo;
    }
}
__END__
[]
[]
[]
[]
[1, 2, 3]
[1, 2, 3]
[1, 2, 3]
[1, 2, 3]
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