Might as well do it on the command line at that point: $ grep '^........k.$' /usr/share/dict/words | grep a | grep b | grep c | grep -v 'a.*a' | grep -v 'b

Might as well do it on the command line at that point: $ grep '^........k.$' /usr/share/dict/words | grep a | grep b | grep c | grep -v 'a.*a' | grep -v 'b.*b' | grep -v 'c.*c' backstroke bailiwicks benchmarks branchlike bushwhacks greenbacks matchbooks piggybacks roadblocks scrapbooks slingbacks throwbacks thumbtacks