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6
Git Log & History Written by Sam Davies & Chris Belanger

You’ve been quite busy in your repository, adding files, making changes, undoing changes and making intelligent commits with good, clear messages. But as time goes on, it gets harder and harder to remember what you did and when you did it.

When you mess up your project (not if, but when), you’ll want to be able to go back in history and find a commit that worked, and rewind your project back to that point in time. This chapter shows you how.

Viewing Git history

Git keeps track of pretty much everything you do in your repository. You’ve already seen this in action in previous chapters, when you used the git log command.

However, there are many ways you can view the data provided by git log that can tell you some incredibly interesting things about your repository and your history. In fact, you can even use git log to create a graphical representation of your repository to get a better mental image of what’s going on.

Vanilla git log

Open your terminal app and execute git log to see the basic, vanilla-flavor history of your repository that you’ve become accustomed to:

commit 477e542bfa35942ddf069d85fbe3fb0923cfab47 (HEAD -> master)
Author: Chris Belanger <chris@razeware.com>
Date:   Wed Jan 23 16:49:56 2019 -0400

    Adding .gitignore files and HTML

commit ffcedc2397503831938894edffda5c5795c387ff
Author: Chris Belanger <chris@razeware.com>
Date:   Tue Jan 22 20:26:30 2019 -0400

    Adds all the good ideas about management

commit 84094274a447e76eb8f55def2c38b909ef94fa42
Author: Chris Belanger <chris@razeware.com>
Date:   Tue Jan 22 20:17:03 2019 -0400

    Removes terrible live streaming ideas

commit 67fd0aa99b5afc18b7c6cc9b4300a07e9fc88418
Author: Chris Belanger <chris@razeware.com>
Date:   Tue Jan 22 19:47:23 2019 -0400

    Moves platform ideas to website directory

Limiting results

This is straightforward; simply execute the following command to show the number of commits you’d like to see, starting from the most recent:

git log -3
git log --oneline
~/MasteringGit/ideas $ git log --oneline
477e542 (HEAD -> master) Adding .gitignore files and HTML
ffcedc2 Adds all the good ideas about management
8409427 Removes terrible live streaming ideas
67fd0aa Moves platform ideas to website directory
0ddfac2 Updates book ideas for Symbian and MOS 6510
6c88142 Adding some tutorial ideas
.
.
.
commit 477e542bfa35942ddf069d85fbe3fb0923cfab47 (HEAD -> master)
477e542 (HEAD -> master) Adding .gitignore files and HTML

Graphical views of your repository

So what else can git log do? Well, Git has some simple methods to show you the branching history of your repository. Execute the following command to see a rather verbose view of the “tree” structure of your repository history:

git log --graph
.
.
.
 commit fbc46d3d828fa57ef627742cf23e865689bf01a0
| Author: Chris Belanger <chris@razeware.com>
| Date:   Thu Jan 10 10:18:14 2019 -0400
|
|     Adding files for article ideas
|
*   commit 5fcdc0e77adc11e0b2beca341666e89611a48a4a
|\  Merge: 39c26dd cfbbca3
| | Author: Chris Belanger <chris@razeware.com>
| | Date:   Thu Jan 10 10:14:56 2019 -0400
| |
| |     Merge branch 'video_team'
| |
| * commit cfbbca371f4ecc80796a6c3fc0c084ebe181edf0
| | Author: Chris Belanger <chris@razeware.com>
| | Date:   Thu Jan 10 10:06:25 2019 -0400
| |
| |     Removing brain download as per ethics committee
.
.
.
* | commit 39c26dd9749eb627056b938313df250b669c1e4c
| | Author: Chris Belanger <chris@razeware.com>
| | Date:   Thu Jan 10 10:13:32 2019 -0400
| |
| |     I should write a book on git someday
| |
* | commit 43b4998d7bf0a6d7f779dd2c0fa4fe17aa3d2453
|/  Author: Chris Belanger <chris@razeware.com>
|   Date:   Thu Jan 10 10:12:36 2019 -0400
|
|       Adding book ideas file
|
* commit becd762cea13859ac32841b6024dd4178a706abe
| Author: Chris Belanger <chris@razeware.com>
| Date:   Thu Jan 10 09:49:23 2019 -0400
|
|     Creating the directory structure
|
* commit 73938223caa4ad5c3920a4db72920d5eda6ff6e1
  Author: crispy8888 <chris@razeware.com>
  Date:   Wed Jan 9 20:59:40 2019 -0400

      Initial commit

git log --oneline --graph
~/MasteringGit/ideas $ git log --oneline --graph
* 477e542 (HEAD -> master) Adding .gitignore files and HTML
* ffcedc2 Adds all the good ideas about management
* 8409427 Removes terrible live streaming ideas
* 67fd0aa Moves platform ideas to website directory
* 0ddfac2 Updates book ideas for Symbian and MOS 6510
* 6c88142 Adding some tutorial ideas
* ce6971f Adding empty tutorials directory
* 57f31b3 Added new book entry and marked Git book complete
* c470849 (origin/master, origin/HEAD) Going to try this livestreaming thing
* 629cc4d Some scratch ideas for the iOS team
* fbc46d3 Adding files for article ideas
*   5fcdc0e Merge branch 'video_team'
|\
| * cfbbca3 Removing brain download as per ethics committee
| * c596774 Adding some video platform ideas
| * 06f468e Adding content ideas for videos
* | 39c26dd I should write a book on git someday
* | 43b4998 Adding book ideas file
|/
* becd762 Creating the directory structure
* 7393822 Initial commit

Viewing non-ancestral history

Git’s not showing you the complete history, though. It’s only showing you the history of things that have happened on the master branch. To tell Git to show you the complete history of everything it knows about, add the --all option to the previous command:

git log --oneline --graph --all
* 477e542 (HEAD -> master) Adding .gitignore files and HTML
* ffcedc2 Adds all the good ideas about management
* 8409427 Removes terrible live streaming ideas
* 67fd0aa Moves platform ideas to website directory
* 0ddfac2 Updates book ideas for Symbian and MOS 6510
* 6c88142 Adding some tutorial ideas
* ce6971f Adding empty tutorials directory
* 57f31b3 Added new book entry and marked Git book complete
* c470849 (origin/master, origin/HEAD) Going to try this livestreaming thing
* 629cc4d Some scratch ideas for the iOS team
| * e69a76a (origin/clickbait) Adding suggestions from Mic
| * 5096c54 Adding first batch of clickbait ideas
|/
* fbc46d3 Adding files for article ideas
*   5fcdc0e Merge branch 'video_team'
|\
| * cfbbca3 Removing brain download as per ethics committee
| * c596774 Adding some video platform ideas
| * 06f468e Adding content ideas for videos
* | 39c26dd I should write a book on git someday
* | 43b4998 Adding book ideas file
|/

Using Git shortlog

Git provides a very handy companion to git log in the form of git shortlog. This is a nice way to get a summary of the commits, perhaps for including in the release notes of your app. Sometimes “bug fixes and performance improvements” just isn’t quite enough detail, you know?

git shortlog
Chris Belanger (18):
      Creating the directory structure
      Adding content ideas for videos
      Adding some video platform ideas
      Removing brain download as per ethics committee
      Adding book ideas file
      I should write a book on git someday
      Merge branch 'video_team'
      Adding files for article ideas
      Some scratch ideas for the iOS team
      Going to try this livestreaming thing
      Added new book entry and marked Git book complete
      Adding empty tutorials directory
      Adding some tutorial ideas
      Updates book ideas for Symbian and MOS 6510
      Moves platform ideas to website directory
      Removes terrible live streaming ideas
      Adds all the good ideas about management
      Adding .gitignore files and HTML

crispy8888 (1):
      Initial commit

Searching Git history

Imagine that you wanted to see just the commits that this crispy8888 fellow had made in the repository. Git gives you the ability to filter the output of git log to a particular author.

git log --author=crispy8888 --oneline
7393822 Initial commit
git log --author="Chris Belanger" --oneline
git log --grep=ideas --oneline
ffcedc2 Adds all the good ideas about management
8409427 Removes terrible live streaming ideas
67fd0aa Moves platform ideas to website directory
0ddfac2 Updates book ideas for Symbian and MOS 6510
6c88142 Adding some tutorial ideas
629cc4d Some scratch ideas for the iOS team
fbc46d3 Adding files for article ideas
43b4998 Adding book ideas file
c596774 Adding some video platform ideas
06f468e Adding content ideas for videos
git log --oneline books/book_ideas.md
57f31b3 Added new book entry and marked Git book complete
39c26dd I should write a book on git someday
43b4998 Adding book ideas file
git log --oneline books
git log --oneline --stat books
ffcedc2 Adds all the good ideas about management
 books/management_book_ideas.md | 0
 1 file changed, 0 insertions(+), 0 deletions(-)
57f31b3 Added new book entry and marked Git book complete
 books/book_ideas.md | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
39c26dd I should write a book on git someday
 books/book_ideas.md | 1 +
 1 file changed, 1 insertion(+)
43b4998 Adding book ideas file
 books/book_ideas.md | 9 +++++++++
 1 file changed, 9 insertions(+)
becd762 Creating the directory structure
 books/.keep | 0
 1 file changed, 0 insertions(+), 0 deletions(-)
git log -S"Fortran"
commit 43b4998d7bf0a6d7f779dd2c0fa4fe17aa3d2453
Author: Chris Belanger <chris@razeware.com>
Date:   Thu Jan 10 10:12:36 2019 -0400

    Adding book ideas file
git log -S"Fortran" -p
commit 43b4998d7bf0a6d7f779dd2c0fa4fe17aa3d2453
Author: Chris Belanger <chris@razeware.com>
Date:   Thu Jan 10 10:12:36 2019 -0400

    Adding book ideas file

diff --git a/books/book_ideas.md b/books/book_ideas.md
new file mode 100644
index 0000000..f924368
--- /dev/null
+++ b/books/book_ideas.md
@@ -0,0 +1,9 @@
+# Ideas for new book projects
+
+- [ ] Hotubbing by tutorials
+- [x] Advanced debugging and reverse engineering
+- [ ] Animal husbandry by tutorials
+- [ ] Beginning tree surgery
+- [ ] CVS by tutorials
+- [ ] Fortran for fun and profit
+- [x] RxSwift by tutorials

Challenges

Speaking of brains, why don’t you exercise yours and reinforce the skills you learned in this chapter by taking on the four challenges of this chapter?

Challenge 1: Show all the details of commits that mark items as “done”

For this challenge, you need to find all of the commits where items have been ticked off as “done”; that is, ones that have an “x” inside the brackets, like so:

Challenge 2: Find all the commits with messages that mention “streaming”

You want to search through the commit messages to find where you or someone else has used the term “streaming” in the commit message itself, not necessarily in the content of the commit. Tip: What was that strangely named command you learned about earlier in this chapter?

Challenge 3: Get a detailed history of the videos directory

For this challenge, you need to show everything that’s happened inside the videos directory, as far as Git’s concerned. But, once again, the basic information about the commit is not enough. You also need to show the full details about that diff. So you’ll tag a familiar option on to the end of the command… or can you?

Challenge 4: Find detailed information about all commits that contain “iOS 13”

In this final challenge, you need to find the commits whose diffs contain the term “iOS 13.” This sounds similar to Challenge 1 above, but if you try to use the same command as you did in that challenge, you won’t find any results. But trust me, there is at least one result in there. Tip: Did you remember to search “all” of the repository?

Key points

  • git log by itself shows a basic, vanilla view of the ancestral commits of the current HEAD.
  • git log -p shows the diff of a commit.
  • git log -n shows the last n commits.
  • git log --oneline shows a concise view of the short hash and the commit message.
  • You can stack options on git log, as in git log -8 --oneline to show the last 8 commits in a condensed form.
  • git log --graph shows a crude but workable graphical representation of your repository.
  • git log --all shows commits on other branches in the repository, not just the ancestors of the current HEAD.
  • git shortlog shows a summary of commits, grouped by their author them, in increasing time order.
  • git log --author="<authorname>" lets you search for commits by a particular author.
  • git log --grep="<term>" lets you search commit messages for a particular term.
  • git log <path/to/filename> will show you just the commits associated with that one file.
  • git log <directory> will show you the commits for files in a particular directory.
  • git log --stat shows a nice overview of the scope and scale of the change in each commit.
  • git log -S"<term>" lets you search the contents of a commit’s changeset for a particular term.

Where to go from here?

You’ve learned a significant amount about how Git works under the hood, how commits work, how the staging area works, how to undo things you didn’t mean to do, how to ignore files and how to leverage the power of git log to unravel the secrets of your repository.

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