Hello Rodster001,

Consider the following test data:

my $names =
[
    {
        id   => 'X01',
        item => 'Widget',
    },
    {
        id   => 'Y02',
        xref =>  12,
        yref =>  13,
    },
    {
        item => 'none',
    },
    {
        id   =>  undef,
    },
];
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This shows two ways in which you may get an undefined value: if the key id exists but the value is undef; and if the key is missing. In both cases, your multi-line code will insert an undef into @ids, which is almost certainly not what you want. (Ok, you may know that your data doesn’t contain any cases like these. But can you be sure that it never will? Defensive programming tests for corner cases and handles them gracefully.) Fix by testing for definedness:

foreach my $a (@{ $names }) {

   push(@ids, $a->{id} // ());
}
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or, using map as per NetWallah++:

my $ids = join ',', map { $_->{id} // () } @$names;
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See perlop#Logical-Defined-Or.

Hope that helps,