Re: [PATCH/RFC 0/4] grep: support to match by line number

[Bert Wesarg <bert.wesarg@googlemail.com>]

On Mon, May 2, 2011 at 13:54, Sverre Rabbelier <srabbelier@gmail.com> wrote:
> Heya,
>
> On Mon, May 2, 2011 at 13:39, Bert Wesarg <bert.wesarg@googlemail.com> wrote:
>> This series will teach git grep to match at specified line numbers. This is
>> particular usefull, if you want to see the lines which emits warnings or errors
>> from a build run (where you only get the line number) and present it nicely to
>> the user with function and context lines.
>
> Can you give a concrete example of how you'd use this? I'm not sure I
> understand the described use case.

I parse the output of compiling a file, there may be warnings or even
errors, I collect the given line numbers, and then call 'git grep -p
-C -n (-@ <lno>)+ -- <path>' to show me what these warnings are about.

For example clang 2.9 (while clang is a bad example, because it prints
the offending line already, but gcc does not generate any warnings on
master currently) gives the following warning (which is probably worth
a patch, btw):

    CC grep.o
grep.c:231:16: warning: comparison of unsigned enum expression < 0 is
always false [-Wtautological-compare]
                if (p->field < 0 || GREP_HEADER_FIELD_MAX <= p->field)
                    ~~~~~~~~ ^ ~
1 warning generated.

I can than call 'git grep -3 -n -h -p -@ 231 -- grep.c', and get:

218=static struct grep_expr *prep_header_patterns(struct grep_opt *opt)
--
228-    for (p = opt->header_list; p; p = p->next) {
229-            if (p->token != GREP_PATTERN_HEAD)
230-                    die("bug: a non-header pattern in grep header list.");
231:            if (p->field < 0 || GREP_HEADER_FIELD_MAX <= p->field)
232-                    die("bug: unknown header field %d", p->field);
233-            compile_regexp(p, opt);
234-    }

Another use case would be to restrict the matching to a block of
lines, this would need the mentioned patch 5, which than will support
line ranges, so that you can say 'match foo, but only in the first 10
lines'.

Bert

>
> --
> Cheers,
>
> Sverre Rabbelier
>