uniq: Fix interactive use.

[des]

Summary

Output a line as soon as it is possible to determine that it will have
to be output. For the basic case, this means output each line as it is
read unless it is identical to the previous one. For the -d case, it
means output the first instance as soon as the second is read, unless
the -c option was also given. The -D and -u cases were already fine.

Add test cases for interactive use with no options and with -d.

Explicitly ignore -d when -D is also specified.

Sponsored by: Klara, Inc.

[kevans]

usr.bin/uniq/uniq.c

140

This is probably worth a small note in the manpage

206

This seems to break the -c -d case:

printf "A\nA\nB\n" | uniq -dc

I'd expect this to print, 2 A, but we don't have any provision in this to output prevline now that we have the final count.

240

The above example is also broken because we shouldn't print here for dflag && cflag unless repeats > 0

[emaste]

usr.bin/uniq/uniq.c

140

Because -D is a superset of -d this behaviour makes sense to me even absent a note in the man page, but I agree it wouldn't hurt to be explicit.

[des]

fix -cd case

[des]

fix markup

[des]

allow -cu, GNU does

[des]

nit

[des]

fix type mismatch

[des]

more nits

[kevans]

usr.bin/uniq/uniq.c

240

The predicates for these are of course an exact match for the mismatch branch above (as well as the show() before the getline loop); might not be a bad idea to pull them out into a macro or inline function (show_every() and show_repeated(repeated) respectively, maybe? *shrug*), but I do not insist