This portal stores URLs with this metadata in several tables. One of these contains "keywords" for each URL in the system (roughly 886 URLs thus far). As the user enters a new URL not in the system, they can enter keywords in that record, so others searching, can find it. The list of keywords is comma-separated in the URL entry form.

My question is, how do I determine that a list of keywords contains duplicates, and remove them, or prompt the user to remove them? For example:

   my @keywords = ('this','that','other','foo','this',              
                   'bar');                      ^dupe
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Obviously this contains a dupe 'this', which should be noted and removed, or pointed out to the user.

Another example:

   my @keywords = ('this','that','other','foo','THIS',
                   'bar');                      ^uc(dupe)
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Also a dupe, 'THIS', though uppercase.

I initially thought lowercasing each word parsed from the list passed, and walking the list, comparing each to the word prior to it, but I don't think that will work for longer lists of keywords.

Has anyone done this before? Any insight as to how this should be designed?

Update:

This code now appears to do what I want, thanks to all who have helped arrive at a solution.

   use strict;

   my (@keywords, %keywords);

   @keywords = ('this', 'that', 'other', 
                'foo', 'THIS', 'bar');
   @keywords{map lc,@keywords}=();
   @keywords = sort keys %keywords;

   foreach my $word (@keywords) {
           print $word . "\n";
   }
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Also, thanks to castaway on CB, this is also in 'perldoc -q duplicate', How can I remove duplicate elements from a list or array?