Re: [PATCH] grep: provide pathspecs/patterns via file or stdin

From: Junio C Hamano <gitster@pobox.com>
Date: Nov 22, 2019, 02:34 UTC
Message-ID: <xmqqwobs7i6u.fsf@gitster-ct.c.googlers.com>
In-Reply-To: <20191122021419.GA52557@generichostname>

Denton Liu <liu.denton@gmail.com> writes:

> The reason I ask is because (correct me if I'm wrong) a lot of other git
> commands (like add, reset and checkout) don't seem to accept pathspecs
> via stdin and could suffer the same problem. xargs seems like a more
> general way of solving the problem of long command lines.

You contributors who are potentially throwing your own topics into the cauldron, please be paying a bit more attention to other topics already cooking in the pot. I think am/pathspec-from-file wants to go in the general direction.

There are things "xargs" is sufficient, and there are things that absolutely requires a single invocation of "git". "grep" is a bit of both.

    $ git grep -e "$pattern" -- A B C

(where A, B and C are hundreds) can be split into three independent invocations of "git grep" via "xargs", essentially running

    $ git grep -e "$pattern" -- A
    $ git grep -e "$pattern" -- B
    $ git grep -e "$pattern" -- C

independently.

But

    $ git grep -e P1 -e P2 -e P3 -- A

(where each of "-e Pn" in reality may be "-e Pn1 -e Pn2 -e Pn3..." that has hundreds of patterns) cannot be split into separate invocations and keep the same meaning.

    $ git grep -e P1 -- A
    $ git grep -e P2 -- A
    $ git grep -e P3 -- A

may show the same lines, but (1) lines with both P1 and P2 would be shown duplicated, and (2) the order of the output would be different from a single invocation looking for all patterns at once.

Needless to say, the ability to combine patterns with --all-match, --and, etc., and negate them would mean the list of patterns must be split (even when it makes sense to do so) at the right places.

    $ git grep -e P1 --and -e P2

cannot be split into two or more invocations, for example.