William Vaughn

The git-log manual review

The git log command is for exploring the history of a git repository. You can use it to visualize, search and explore the unique story which has lead to the current state of the code. Personally, the most common ways I’ve used git log are to review my last few commits and to see the commits I’ve made since a branch diverged from master.

git log master..HEAD

This is a one-dimensional and basic usage of git log, and that has been perfectly fine for me. This is, quite frankly, all I have ever needed. Part of my journey though the git manuals is to re-discover familiar commands while looking for new ways to apply them in my workflow. I certainly learned a few things that I will be looking to employ as I see opportunities. I hope you’ll learn something from this review as well!

Basics

Visualize the whole network of changes

The log can all but replace the github network page, or fancy proprietary git GUI tools.

 git log --all --graph

This is remarkably good for visualizing the basics of whose doing what, and where. I can imagine in very large projects this view could get a bit unwieldy, in which case you’ll need to use it with some surgery. In normal size projects this is a good way to quickly get your bearings.

It’s worth a note that the --decorate option which shows the full ref names for every commit is enabled by default. Ignoring the reasons for why one would want to turn them off, there is the --no-decorate option which does allow for turning them off.

Hide the merge commits --no-merges

There are times when seeing how branches have been merged into each other is useful, but much of the time this is just noise. Filter out the noise:

 git log --no-merges

Evolution of file(s)

You can easily see a list of commits which affected the given path(s).

git log ./README.md

It’s a bit trickier when a file has changed locations of course, but git log has your back with the --follow option which will follow file movements.

Tracking changes of line numbers or functions

You want to know how a certain section of a file changed.

 git log -L 1,20:app.py

Show every commit, and diffs for them, which makes an alteration to the first 20 lines of a python file. Probably going to consist of changes that document every time you made new imports. :)

You can also look at commits which alter a particular function in a file.

 git log -L :create_app:app.py

This will show all commits which affected the create_app function. Extremely useful!

Basic output formatting --pretty

The above commands automatically shows the full diffs for each commit, but if you want to see a more concise summary of each commit the commit formatting and diff options of git log are invaluable.

You can use -s, --no-patch to suppress the diff output entirely.

 git log --no-patch -L :create_app:app.py

To format the commits, the --pretty options are really convenient. The options in increasingly more verbose order are oneline, short, medium, full, fuller, email, raw. You can also of course set your own formats.

 git log --no-patch --pretty=oneline -L :create_app:app.py

Commit limiting

Along with being able to define ranges of commits using normal gitrevisions techniques, the git log command offers additional ways to further limit the displayed objects.

Exploring by date with --since and --until

Here’s one for the overzealous managers out there (not that you would ever read blogs about the git manual): every commit your dev team made in Q1 this year.

git log --since=2019-01-01 --until=2019-04-01 --no-merges

This shows them in reverse chronological order though, no executive is going to want to look at it like that. So we will flip them

git log --since=2019-01-01 --until=2019-04-01 --no-merges --reverse

These options are also available under the aliases --after and --before.

Exploring by --author

What has she ever done?

git log --author='Ada Lovelace'

Searching your log messages --grep

All the commits which contain the substring “separate”.

git log --grep=separate

Using some regex, let’s see only the ones that start with “separate”, but let’s also throw in the fact that we often don’t spell that word correctly.

git log --perl-regexp --regexp-ignore-case --grep='^sep[ae]rate\s'

Conclusion

I really enjoyed learning more about git log and I hope that it prompts me to ask more interesting questions of my repositories. All the best! Thanks for reading the manual review!