Less is more - Limit the size of your Git log output

In the previous post, we learned how to customise the output of the git log command. That post dealt with the presentation of the logs.

When we run the git log command, we generally do it to answer a question that we have. Those questions can be anything:

• When was this function last changed?
• What were the last 3 commits?
• What were the commits done by the X co-worker?
• Any other question

Essentially, log of all the commits is generally useless to us. We, often, only need a subset of the log to find an answer to our questions. In this post, I will introduce you to some of the options supported by git log that helps us limit the number of commits that are displayed.

View the last n commits

You can use git log -<n>, where n is any integer to show the last n commits. For example, running git log -3 will return the last 3 commits in the log.

View the commits made since X date

You can use git log --since=<date>, where date is either a specific date (like 2023-06-22 in YYYY-MM-DD format) or a relative date (like "2 days 1 hour ago") to show all the commits made since a certain date. For example, running git log --since="2 days ago" will return all the commits made in the last 2 days.

I encourage you to explore man git-log to learn about other formats supported by the --since flag.

View the commits whose patch contains X string

Often times, you need to search for a commit whose patch contains a certain string. For instance, you may be want to know which commit changed the API error message in your code.

The -S flag can be used to search for commits whose patch contains a certain string. In order to view what exactly matched, this flag is best used with the --patch (-p) flag.

For example, running git log -S "error" will return all the commits whose patch contains the string "error". The output of the command git log -S "change" -p is shown below. Notice the string "change" in the last line of the diff output.

commit 596cb31a2d6e961ebc1fd413a384c342e19543f5
Author: Ayush Poddar <[e-mail]>
Date:   Thu Jul 27 10:40:19 2023 +0530

    Update bat.md

diff --git a/bat.md b/bat.md
index a5c1966..6dda867 100644
--- a/bat.md
+++ b/bat.md
@@ -1 +1,3 @@
 Hello, world
+
+Making a change after removing it from index in local

View the commits where a specific file(s) changed

You may be wanting to view the commits where a certain file/files was/were changed. The command looks like this: git log -- <filepath>, where filepath can be the path to files you are investigating. The -- (double dashes) is used to separate the options provided to git log from <filepath>. If a list of file paths are provided, then all the commits where ANY one of the files was changed is returned. It basically acts as a OR matcher instead of AND matcher.

For example, the sample output of running git log --stat -- ammend.md foo.txt is shown below. I have used the --stat option so that I can show you that only the commits where either ammend.md OR foo.txt changed are outputted.

commit 1062877fc12c3b3d54ca17f539abc71ccb3cc324
Author: Ayush Poddar <[e-mail]>
Date:   Wed Aug 9 09:47:20 2023 +0530

    some change

 foo.txt | 1 +
 1 file changed, 1 insertion(+)

commit 596cb31a2d6e961ebc1fd413a384c342e19543f5
Author: Ayush Poddar <[e-mail]>
Date:   Thu Jul 27 10:40:19 2023 +0530

    Update bat.md

 ammend.md | 3 +++
 1 file changed, 3 insertions(+)

More options

git log supports more options. The best way to explore them would be to use man git-log. Here are some of the most common ones:

Option	Description
-<n>	Show only the last n commits.
--since, --after	Limit the commits to those made after the specified date.
--until, --before	Limit the commits to those made before the specified date.
--author	Only show commits in which the author entry matches the specified string.
--committer	Only show commits in which the committer entry matches the specified string.
--grep	Only show commits with a commit message containing the string.
-S	Only show commits adding or removing code matching the string.

It is possible to specify more than one instance of --grep and --author search criteria. In other words you can do this: git log --grep foo --author Ayush --grep bar --author Candy. In such cases, the output will be those commits which match ANY of the authors provided and ANY of the grep patterns.
If you want commits which match ALL the grep patterns provided, then you can use the --all-match flag. For example: git log --all-match --grep foo --grep bar will output all commits whose commit messages contain both foo AND bar.
--all-match only works for --grep. In fact, you do not need it for --author since any commit will have only one author.

Final words

A key part of root cause investigations is browsing your Git logs. You go through the Git logs to figure out which exact change caused the bug and why was the change made.

Now you are in the position to do so more efficiently. You can use a combination of the options shown in this post and the previous post to speed up your investigations.

Source

• https://git-scm.com/book/en/v2/Git-Basics-Viewing-the-Commit-History