The problem with using the  || (logical-or) operator (see perlop) in this case is that the undefined value is false, as are 0, '0' and '' (the empty string), and  || does not distinguish. If your Perl version is 5.10+, you can use the  // (defined-or) operator; otherwise, you're stuck with syntax that's a bit more messy:

c:\@Work\Perl\monks>perl -wMstrict -le
"use 5.010;
 ;;
 my @ra = (0, 0, 0);
 ;;
 my $i = 1;
 print qq{value at index $i: }, $ra[$i] || 'undef';
 print qq{value at index $i: }, $ra[$i] // 'undef';
 print qq{value at index $i: }, defined($ra[$i]) ? $ra[$i] : 'undef'
"
value at index 1: undef
value at index 1: 0
value at index 1: 0
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