thanks - it's been a while :)

I eventually ended up with the following: 

my $unique = qr/^(.)(?!\1)
                 (.)(?!\1|\2)
                 (.)(?!\1|\2|\3)
                  .$/x;

[download]
   larryk                                          
perl -le "s,,reverse killer,e,y,rifle,lycra,,print"

In reply to Re^2: How to use a negative backreference in regex? by larryk
in thread How to use a negative backreference in regex? by larryk

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