Re: tests/yesno.sh, kinds of line (matching/non-matching, selected/rejected)

[Julian Foad]

Charles Levert wrote:
> * On Sunday 2005-11-13 at 18:44:57 +0000, Julian Foad wrote:
> > > Test #28:  { ../src/grep -F -n -b -m 2 -v -C 1 -o yes; echo "?$?"; sed 
> >
> > We'll discuss the interaction between "-v" and "-o" separately.
>
> Test #28 still involves a context line (albeit
> here a matching one, since -v), so whatever
> decision is made for the other two tests should
> equally apply here (regarding -C/-m).

Well, the decision made about -C/-m _affects_ this test but is not the only 
consideration, because of the additional "-v".

> As for -C/-v/-o and the warning issue, I think
> we do disagree.  With -o, I see a line-group
> (including selected and context lines) as a
> pool of _printable_ content, i.e., lines to scan
> for -o parts.  Hence, I see no special case or
> need for a warning then, and I see the group
> separator remaining.   -C/-v/-o means "find all
> matching parts in the vicinity of a non-matching
> line (or lines) and collect them as a group".

Yikes.  There's some kind of logic to that line of reasoning, but it strikes me 
as very arcane.  I have never thought of wanting such output.  I can't imagine 
any meaningful use for it.  Sorry.  That logic involves Grep doing two 
different kinds of search (conceptually, not just implementation-wise which it 
currently does anyway).  That effect is much better and more flexibly obtained 
with two successive Greps: "grep -C -v | grep -o".

I think "-v" and "-o" are mutually exclusive:

  -v: "show only the lines that have no matches"
      (possibly with a few lines of context)

  -o: "show only the matches"
      (it would make some kind of logical sense to show possibly a few 
_characters_ of context around each match, but nobody has asked for that)

I'm greatly in favour of options having orthogonal meanings as much as 
possible, but I it is unreasonable here.  It is far better to disallow certain 
combinations (which can then be given meanings in the future if it becomes 
desirable) than to give them a meaning now just because we can (and then have 
to support that meaning forever even though it is not useful).

Hey, there's another example of keeping it free of unneeded functionality and 
future-proof: we don't support context lines with "-o".  If we were to make 
"-C" work with "-o" in some arbitrary line-based way now, we'd lock ourselves 
out of the possibility of making it show the specified number of _characters_ 
if and when people do start to expect that.  (I'd never thought of that 
"characters of context" idea until now, and I don't know if it will ever be 
wanted, and don't suggest we even consider implementing it, but it illustrates 
a point.)


> > That means those "4/..." tests are wrong.
>
> Since yesno.sh specializes in exactly this
> kind of issues, should we now just remove those
> from foad1.sh?  Or do still they do something
> for anchors that nothing else does?

Their original purpose, as I mentioned, was to check that Grep doesn't crash. 
The appropriate way to do this would be to change them to not check the output; 
one of the other test files may have a more appropriate framework for doing that.

- Julian