How to grep Git commit diffs or contents for a certain word?

Question

In a Git code repository I want to list all commits that contain a certain word. I tried this

git log -p | grep --context=4 "word"

but it does not necessarily give me back the filename (unless it's less that 5 lines away from the word I searched for. I also tried

git grep "word"

but it gives me only present files and not the history.

How do I search the entire history so I can follow changes on a particular word? I intend to search my codebase for occurrences of word to track down changes (search in files history).

Answer 1

If you want to find all commits where commit message contains given word, use

$ git log --grep=word

If you want to find all commits where "word" was added or removed in the file contents (to be more exact: where number of occurences of "word" changed), i.e. search the commit contents, use so called 'pickaxe' search with

$ git log -Sword

In modern git there is also

$ git log -Gword

to look for differences whose added or removed line matches "word" (also commit contents).

Note that -G by default accepts a regex, while -S accepts a string, but can be modified to accept regexes using the --pickaxe-regex.

To illustrate the difference between -S<regex> --pickaxe-regex and -G<regex>, consider a commit with the following diff in the same file:

+    return !regexec(regexp, two->ptr, 1, &regmatch, 0);
...
-    hit = !regexec(regexp, mf2.ptr, 1, &regmatch, 0);

While git log -G"regexec\(regexp" will show this commit, git log -S"regexec\(regexp" --pickaxe-regex will not (because the number of occurrences of that string did not change).

---

With Git 2.25.1 (Feb. 2020), the documentation is clarified around those regexes.

See commit 9299f84 (06 Feb 2020) by Martin Ågren (``).
^{(Merged by Junio C Hamano -- gitster -- in commit 0d11410, 12 Feb 2020)}

diff-options.txt: avoid "regex" overload in example

^{Reported-by: Adam Dinwoodie
Signed-off-by: Martin Ågren
Reviewed-by: Taylor Blau}

When we exemplify the difference between -G and -S (using --pickaxe-regex), we do so using an example diff and git diff invocation involving "regexec", "regexp", "regmatch", ...

The example is correct, but we can make it easier to untangle by avoiding writing "regex.*" unless it's really needed to make our point.

Use some made-up, non-regexy words instead.

The git diff documentation now includes:

To illustrate the difference between -S<regex> --pickaxe-regex and -G<regex>, consider a commit with the following diff in the same file:

+    return frotz(nitfol, two->ptr, 1, 0);
...
-    hit = frotz(nitfol, mf2.ptr, 1, 0);

While git log -G"frotz\(nitfol" will show this commit, git log -S"frotz\(nitfol" --pickaxe-regex will not (because the number of occurrences of that string did not change).