dups is indeed a little helper of mine. Like uniq it only handles sorted input. Update: I see you edited your answer to include uniq -d. I wasn't aware of the option, thanks. Now I can simplify the implementation of dups. But I find the name valuable, and I think it's perverse to say uniq when you mean its opposite.
The input file is reliably the second word, so C-A M-f gets me to it if I want to operate on a different file. !!:1 gets me the file if I want to use it in a new command.
1. cat file
2. cat < file
3. echo abc|cat
4. echo abc|cat - file
cat can take input from the left, the right, or both
same goes for cut
I could keep the file first by saying:
$ < combo_not.txt cut -c7-40 |sort |dups |wc -l
Perhaps we should stop here. You seem to have made this account just a few hours ago for the express purpose of poking at people's code fragments in this thread. You're making stylistic nitpicks (they don't affect correctness, do they?) and you're making them in a tone that I'm not sure I would take from Randal Schwartz himself (you actually edited http://news.ycombinator.com/item?id=4076556 to be ruder than the original). It's a drag, man.
cut -c4-70 combo_not.txt|...
BTW, HN has some formatting support: http://news.ycombinator.com/formatdoc