[lmi] It this temporary file good, or bad?

[Greg Chicares]

Vadim--Please consider commit ae17ea6bdfdc, which adds this
makefile target:

show_overlooked_cxx_warnings:
       @$(CXX) $(ALL_CXXFLAGS) -Q --help=warning -xc++ /dev/null \
         | $(GREP) '[[]disabled[]]' \
         | $(SED) -e's/[ \t]*[[]disabled[]]//' -e's/^ *-W//' \
         > eraseme
       @$(GREP) -of eraseme $(this_makefile) | $(GREP) -vxf - eraseme || true
       @$(RM) eraseme

It seems to work just fine, but it troubles me that I couldn't
find a way to do this without a temporary file. Isn't there a
better, more unixy way that avoids that file? Reusing the same
stream twice seems to call for 'tee', but I don't see how to
make it work here.

Let me try to draw a picture of what I was hoping to do:

  cmd | tee >>>>> "grep -oF - workhorse.make" +
              |                               |
              >>>>>>>>>>>>>        <<<<<<<<<<<<
                          |        |
              grep -vf stream#1 stream #2 --> output

It's easy enough to split the stream into two rivulets with 'tee';
what I can't figure out is how to recombine the two rivulets as
arguments in the final grep command. This is tantalizingly close
to common examples like:

  diff <(sort file1) <(sort file2)

but I seem to be missing the magic glue to put it together.

What would a unix master do?