Does it mean that one of the @CHOICE array contents are empty?

Yes. You can avoid that warning by checking for definedness:

foreach (@CHOICE) {
    if (defined && m/2001\sCensus\sOutput\sArea/){
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foreach (@CHOICE) {
  next if (!defined);
  if (m/2001\sCensus\sOutput\sArea/){
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This uses $_ implicitly in both the definedness test and the pattern match. Often it's clearer to assign the value to a lexical variable:

for my $chosen (@CHOICE) {
    if (defined $chosen && $chosen =~ m/2001\sCensus\sOutput\sArea/){
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As a further comment, usage of upper-case variable names is generally reserved for constants or perl private variables.

And since the pattern can never match the empty string, or 0, you could skip the define and write:

    foreach (@CHOICE) {
        if ($_ && /.../) { ... }
    }
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Or:

    foreach (@CHOICE) {
        $_ or next;
        if (/.../) { ... }
    }
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if all you have inside the foreach is the if statement.
Perl --((8:>*

I don't particularly want to argue about it but I would not approve of such a change. True, as the pattern match is now it does not make a difference, but if the pattern is ever changed it's easy to miss changing the test as well, which can introduce a subtle bug. Just checking for truth makes the code more brittle. IMO, YMMV, etc.


There are ten types of people: those that understand binary and those that don't.

If the @CHOICE array was empty, the loop would never get executed. However, it is very likely that (at least) one of the elements of @CHOICE is undefined. Maybe you should show us a little bit more of your code.

I use the supper search every night. Last night it found me some tasty Chinese food.

Asking the Wise Monks(reg) to explain odd aspects of perl is generally a Wise Move(reg), but I wonder if it's the most time-efficient way of answering your question.

I would have suggested altering the script to place a print statement or two at that point:

foreach (@CHOICE) {
    print "\$_ is ", ( defined $_ ? "'$_'.\n" 
                     :              "undefined.\n"
                     );
    if ($_ =~ /2001\sCensus\sOutput\sArea/){
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Or ( my preference ) run the program in the debugger, and find out what's happening at that point.