# git diff -G: Regex pattern to exclude a word

2 messages from 2025-01-29 to 2025-01-29. Participants: Raghavendra N, Chris Torek.
Thread: https://gitlist.dev/t/62865

## Raghavendra N, 2025-01-29 06:05

Subject: git diff -G: Regex pattern to exclude a word
Message-ID: <CA+U2-7GiHq9qhiyLPLgzOd1JK072gzkmZ+4vQ11V0QpKgPif=Q@mail.gmail.com>
URL: https://gitlist.dev/e/CA%2BU2-7GiHq9qhiyLPLgzOd1JK072gzkmZ%2B4vQ11V0QpKgPif%3DQ%40mail.gmail.com

```
Dear Members,

TL;DR: Question is - How to use the -G option in git diff to exclude a word?

I'm trying to understand how the -G option in git diff works.
Specifically I'm trying to test a Regex which excludes a word from the
git diff.

Consider the following setup:

    > git diff
    first-file.txt
    @@ -1 +1 @@
    -Lorem Ipsum is simply dummy text.
    +Lorem Ipsum is simply dummy text. tree

    second-file.txt
    @@ -1 +1 @@
    -Lorem Ipsum is simply dummy text.
    +Lorem Ipsum is simply dummy text. ball

Word "tree" is added in the first-file.txt and word "ball" is added in
the second-file.txt.

If I run this `git diff -G "^.*tree.*"`, it shows only the first-file.txt.

    > git diff -G "^.*tree.*"
    first-file.txt
    @@ -1 +1 @@
    -Lorem Ipsum is simply dummy text.
    +Lorem Ipsum is simply dummy text. tree

This is correct because the Regex is checking if textual diff has an
added or a deleted line that includes a word "tree".

Now if I try to exclude the word "tree" with this Regex
"^([^t]|(t[^r])|(tr[^e])|(tre[^e]))*($|(t($|(r($|e$)))))", it should
only show the second-file.txt. But the diff lists both the files.

    > git diff -G "^([^t]|(t[^r])|(tr[^e])|(tre[^e]))*($|(t($|(r($|e$)))))"
    first-file.txt
    @@ -1 +1 @@
    -Lorem Ipsum is simply dummy text.
    +Lorem Ipsum is simply dummy text. tree

    second-file.txt
    @@ -1 +1 @@
    -Lorem Ipsum is simply dummy text.
    +Lorem Ipsum is simply dummy text. ball

So the question is how does the -G option work in this case? And how
to use the -G option to exclude a word?

Thanks,
Raghavendra

```

## Chris Torek, 2025-01-29 11:01

Subject: Re: git diff -G: Regex pattern to exclude a word
Message-ID: <CAPx1Gvf+80Yty1R3O766fwYiRUysQ3Ss1XbFq7hmrfcUcawBAA@mail.gmail.com>
URL: https://gitlist.dev/e/CAPx1Gvf%2B80Yty1R3O766fwYiRUysQ3Ss1XbFq7hmrfcUcawBAA%40mail.gmail.com
In-Reply-To: <CA+U2-7GiHq9qhiyLPLgzOd1JK072gzkmZ+4vQ11V0QpKgPif=Q@mail.gmail.com>

```
On Tue, Jan 28, 2025 at 10:05 PM Raghavendra N <nraghavendra89@gmail.com> wrote:
> I'm trying to understand how the -G option in git diff works.
> Specifically I'm trying to test a Regex which excludes a word from the
> git diff.

"Inverting" a regular expression is technically always possible,
but is difficult to get right, and I think you made a slight error in
your attempt. See also https://www.vidarholen.net/contents/blog/?p=36
(which has a link to a Haskell program to generate an inverted regex
automatically).

With `git grep` you can specify perl-style regular expressions,
which allow negative lookahead, but `git diff -G` does not
support that. See
https://stackoverflow.com/questions/39789921/what-flavor-of-regex-does-git-use
for details.

I think it would be nice to add some of `git grep`'s options to
`git diff` here, but I leave that as an exercise. :-)

Chris

```