* On Tuesday 2005-08-23 at 16:24:05 +0200, Stepan Kasal wrote:
>
> Sure, I understood that. That's what
> sed 's/a*/X/g'
> or
> awk 'gsub(/a*/,"X")'
> does.
>
> Your arguments seem to show that grep should print only lines
> with _nonempty_ matches. (Empty pattern might be an exception.)
> But that's too late to change.
Hmmm. I may require more thought before we
commit to anything. To state explicitly what
you probably already understood (I'm thinking out
loud here), the way grep currently works is:
-- To first identify which lines contain
matches (both empty and non-empty) so
that in the case of a 'a*'-type pattern,
every line will match at that step.
I assume that's the part you say is too
late to change.
-- Then, since there are no non-matching
lines in that case anyway, all line are
screened for matches to display in both
the --only-matching and --color cases
(otherwise they are just displayed right
away). The question at this step is only
non-empty matches or all matches regardless
of their length.
> With current setup, the inconsistency will show up because
> grep --colour 'a*'
> will then print lot of lines without any colour tags.
> It might be confusing for X-ray robots who expects to see the
> tags...
Especially for non-empty matches.
> I wanted to prefer consistency. Then I'd have to teach people that they
> shouldn't use patterns which match empty string.
Indeed, that's what users should really do.
Let's warn about it in the docs.
> You wanted to change the specification of --only-matching (--colour),
> so that it prints (colorifies) only non-empty matches.
Yes. Note that there is in fact no specification
since this is a GNU extension that POSIX or
others don't know or say anything about.
Hence probably the current implementation
which also shows the inconsistency, but with a
difference in degree.
> OK, I no longer object to it. But please change the decumentation
> (info and manpage) so that it states this clearly.
Ok. I will put this under --only-matching and --color.
