How can grep commits be based on a certain string?

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).

A few things to note:

  • -G by default accepts a regex, while -S accepts a string, but it can be modified to accept regexes using the --pickaxe-regex.
  • -S finds commits where the number of occurrences of “word” changed, while -G finds commits where “word” appears in the diff.
  • This means that -S<regex> --pickaxe-regex and -G<regex> do not do exactly the same thing.

The git diff documentation has a nice explanation of the difference:

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).

This will show the commits containing the search terms, but if you want to see the actual changes in those commits instead you can use --patch:

$ git log -G"searchTerm" --patch

This can then be piped to grep to isolate the output just to display commit diff lines with that search term. A common use-case is to display diff lines with that search term in commits since and including a given commit – 3b5ab0f2a1 in this example – like so:

$ git log 3b5ab0f2a1^.. -G"searchTerm" --patch | grep searchTerm

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