% perl -nwle 'END{ warn +(times)[0],"\n" }
  print $_
' /usr/share/dict/hv.words | wc -l
0.04
285520
% perl -nwle 'END{ warn +(times)[0],"\n" }
  print $_ if /^(.)(?!\1)(.)(?!\1|\2)(.)(?!\1|\2|\3)(.)(?!\1|\2|\3|\4)(.)$/
' /usr/share/dict/hv.words | wc -l
0.13
8632
% perl -MList::MoreUtils=uniq -nwle 'END{ warn +(times)[0],"\n" }
  print $_ if /^(?:(.)(.)(.)(.)(.)(?(?{ 5 != uniq $1, $2, $3, $4, $5 })(?!)))$/
' /usr/share/dict/hv.words | wc -l
0.39
8632
% perl -MList::MoreUtils=uniq -nwle 'END{ warn +(times)[0],"\n" }
  print $_ if /^(.)(.)(.)(.)(.)$/ && 5 == uniq $1, $2, $3, $4, $5
' /usr/share/dict/hv.words | wc -l
0.1
8632
% 

##</code><code>##

% perl -MList::MoreUtils=uniq -nwle 'END{ warn +(times)[0],"\n" }
  print $_ if /^(?:(.)(.)(.)(.)(.)$(?(?{ 5 != uniq $1, $2, $3, $4, $5 })(?!)))/
' /usr/share/dict/hv.words | wc -l
0.12
8632
%