From a practical standpoint, you cannot rely on users to fill in a textarea in any consistent way. Even if you give clear insteructions and they want to do it right, you'll get some mighty bizarre data. A textarea's data comes back as a single string, so the unforgiving way to parse out an array of values like you show is:

use strict;
use CGI;
my $query = new CGI;

my @ary = ($query->param('the_textarea')) =~ m/([A-Z]{3}\d{4})/gs;
print '||',join('||', @ary),'||';
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You are using CGI.pm aren't you?

Update: Fixed typo in @ary assignment. Thanks jlongino for sharp eyes and kind acts.

After Compline,
Zaxo