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

If you want to find all commits where the commit message contains a 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 the number of occurrences of "word" changed), i.e., search the commit contents, use a 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 it 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 the 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", etc.

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).

git log's pickaxe will find commits with changes including "word" with git log -Sword

After a lot of experimentation, I can recommend the following, which shows commits that introduce or remove lines containing a given regexp, and displays the text changes in each, with colours showing words added and removed.

git log --pickaxe-regex -p --color-words -S "<regexp to search for>"

Takes a while to run though... ;-)