Everything I've Learned About Git
in the Last Year

(So You Don't Have To)

Trevor Burnham / @trevorburnham

The Theme of This Talk

Git is wonderful.
Unfortunately, Git doesn't like you.

Git’s command names are lies.
Its output is cold and unfeeling.
And have you read those man pages?

The Theme of This Talk

Fortunately, I like you!
And I know, like, 20% of git.
This will be an infodump.

Git Wants You to Fight It

But You Can Be Friends!

How?

Use good tools.
Understand Git’s fundamental concepts.
Know what every command you run actually does.

Setting Up

Install the Latest


$ brew update
$ brew upgrade git

Yes, hub will wrap around the new version:


$ hub --version
git version 1.8.3.2
hub version 1.10.6

Git-ify Your Shell Prompt

Set Your Editor


# ~/.gitconfig
[core]
	editor = subl -w

Classy way:
git config --global core.editor "subl -w"
Alternatively, you can set your shell's GIT_EDITOR.
Or just EDITOR.
subl needs the -w flag to block Git until you close the tab.

Use Your Freedom of Choice

Get a Git Gutter

https://github.com/jisaacks/GitGutter

Run (Some) Git Commands

https://sublimegit.net/

Configuring Git

The settings in a repo's .git/config override those in ~/.gitconfig when you're in that repo.
You can see all applicable settings with
git config --list.
git config namespace.key value sets a value in .git/config.
Add the --global flag to modify ~/.gitconfig instead.

Example: Setting Your Name and Email


$ git config --global user.name "Your Name"
$ git config --global user.name "[email protected]"  # public!

https://help.github.com/articles/keeping-your-email-address-private

Example: Adding a Global Gitignore


# ~/.gitignore_global
.DS_Store


$ git config --global core.excludesfile ~/.gitignore_global

https://help.github.com/articles/ignoring-files

Example: Setting an Alias


$ git config --global alias.unstage "reset HEAD"


$ git unstage some_file  # git reset HEAD some_file

History of Git


$ git log --full-history --reverse

Version Control for Linux

First Commit

commit e83c5163316f89bfbde7d9ab23ca2e25604af29
Author: Linus Torvalds <[email protected]>
Date: Thu Apr 7 15:13:13 2005 -0700
Initial revision of "git", the information manager from hell

Totally Distributed

Git vs. Mercurial

Why Git Won

I got 99 problems, but at least I don't have to use BitBucket

So…What is Git?

It's All About the Commits

Get to know git show.

One Hash Unlocks the Entire Universe!

Hashcapades: The art of the perfect hash adventure

Can't Hashes Conflict?

“A higher probability exists that every member of your programming team will be attacked and killed by wolves in unrelated incidents on the same night.”

—Pro Git

What's a Branch?

“A branch is just a pointer to a commit.”

Huh! Then What's a Tag?

“A tag is just a pointer to a commit.”

Why Use Branches?

Branch names tell you what you're supposed to be working on

What is the HEAD?

Put the HEAD on the part of the record you want to play

Moving the HEAD


(master) $ git checkout HEAD^  # parent commit
(fc8a3b) $


(master) $ git checkout HEAD~1  # equivalent
(fc8a3b) $

There ought to be only one way to do it!

Checkout vs. Reset

“…update HEAD to set the specified branch as the current branch.”

—git help checkout

“…set the current branch head (HEAD) to <commit>…”

—git help reset

Pointers are Hard!


(master) $ git reset --hard HEAD~1
# changes what master points to!
(master) $ nooooooooooooo!! what was my hash!?
> command not found


(master) $ git reflog
> 2e22821 HEAD@{0}: reset: moving to HEAD~1
> 62fb09e HEAD@{1}: checkout: moving from 69a077 to master
(master) $ git reset --hard 62fb09e  # fixed!

Staging and Committing

A Tale of Two Directories

Working tree: The physical directory you've cd-ed to, and everything in it.

Except the .git directory.
FOR THE SAKE OF ALL THAT IS GOOD AND HOLY, DO NOT TOUCH .git!!!

Unless you're editing .git/config. That's cool.

Index: Also known as the staging area. This is everything that will be in the next commit.

Make New Commits, But Keep The Old


(7e8fcg) $ git add README.md
# stage the current state of README.md
(7e8fcg*) $ git commit
# create a new commit with that one difference
(89a2bd) $

PSA: Life's too short to use git add <file>.

All the World's Staged


(master*) $ git add -A
# stage every indexed file in the working directory
(master*) $ git commit
(master) $

This won't stage any files in the HEAD's .gitignore. Then Git's like, "Changes? I don't see any changes!"
Likewise if you've done something crazy like git update-index --assume-unchanged <file>.


(master*) $ git commit -a
# equivalent to the above in just one step
(master) $

You Only Live Once

Unstaging


(master*) $ git reset HEAD README.md
# unstage, don't change the working directory


(master*) $ git checkout HEAD -- README.md
# unstage and restore the HEAD version of README.md

Why does git checkout -- README.md restore the HEAD version of README.md if it's unstaged, but has no effect if it's staged?
Because the git checkout defaults to using the index.

What Have I Done?


(master*) $ git status


(master*) $ git diff  # show unstaged changes


(master*) $ git diff --cached  # show staged changes


$ alias what-am-i-about-to-commit "git diff --cached"

Pro Tip: Verbose Commit


(master*) $ git commit --verbose

Communicating with Remotes

Managing Remotes


(master) $ git remote  # use --verbose to see URLs
origin


(master) $ git remote add other git://github.com/otherguy/project.git


(master) $ git remote rm other

Tracking Branches


(master) $ git branch
master


(master) $ git branch -r
origin/master
origin/feature


(master) $ git branch feature origin/feature

feature is now tracking origin/feature.

Pull vs. Fetch


(master) $ git fetch origin  # update origin/x branches


(master) $ git pull origin   # for each origin/x branch, update and merge into x

My Favorite Aliases


alias ggpull="git pull origin $(current_branch)"
alias ggpush="git push origin $(current_branch)"

What's a Merge, Really?

The Simple Case

		1--2--+         master
		      |
		      3--4      feature


(master) $ git merge feature

		1--2--3--4      master

This is a fast-forward. Don't do this.

The Simple Case, Redux

		1--2--+         master
		      |
		      3--4      feature


(master) $ git merge --no-ff feature

		1--2--+-----5   master
		      |     |
		      3--4--+

5 is a merge commit. Merge commits are your friend, because you can revert them in one command:
git revert -m 1 <commit>

The Complicated Case

		1--2--3--4   master
		   |
		   +--5--6   feature


(master) $ git merge feature

		      3--4
		      |  |
		1--2--+  +--7   master
		      |  |
		      5--6

This is a three-way merge.
The three "ways" are commits 4, 6, and 2.

Two Parents!?

		      3--4
		      |  |
		1--2--+  +--7   master
		      |  |
		      5--6

Commit 7 is a merge commit with two parents. The one that was originally on master (commit 4) gets to be the first parent.


(commit7) $ git checkout HEAD^
(commit4) $


(commit7) $ git checkout HEAD^2
(commit6) $

The Wrong Way To Log


(master) $ git log


(master) $ git checkout HEAD~2
(d2e7d2) $ WTF? The log said this was 3 commits ago!!
> command not found

The Pretty Way To Log


(master) $ git log --graph

The Right Way To Log


(master) $ git log --first-parent

Enter Rebase

Rewriting History

		1--2--3--4      master
		   |
		   +--5--6      feature


(feature) $ git rebase master

		1--2--3--4        master
		   |
		   +--3--4--7--8 feature

Commits 7 and 8 are copies of commits 5 and 6 with different ancestries and commit timestamps.

The Awesomest Git Command Ever

		1--2--3--4      master
		   |
		   +--5--6      feature


(feature) $ git rebase -i master


pick f8fcfe4 Add icons
pick b2a339f Fix typo

# Commands:
#  p, pick = use commit
#  r, reword = use commit, but edit the commit message
#  e, edit = use commit, but stop for amending
#  s, squash = use commit, but meld into previous commit
#  f, fixup = like "squash", but discard this commit's log message
#  x, exec = run command (the rest of the line) using shell
#
# These lines can be re-ordered; they are executed from top to bottom.
#
# If you remove a line here THAT COMMIT WILL BE LOST.

Pro Tip: Rebase on Pull


$ git config --global pull.rebase true

No more superfluous merge commits on pull!
Caution: If there are conflicts, abort! Use
git pull --no-rebase to override the default.

More Tools

Fix Your Last Commit


(master) $ git commit -m "Lame commit message"
(master) $ git commit --amend


(master*) $ git commit -m "Oops, forgot to add README.md"
(master) $ git add README.md
(master) $ git commit --amend

Track Down Bugs with Bisect


(master) $ git bisect start  # There's a bug!
(master) $ git bisect bad    # It's on master!


(master) $ git checkout HEAD~64
(f8b451) $ git bisect good   # This commit doesn't have the bug!


(b8cfas) $ git bisect reset  # Bad commit found. Now let's fix it.

Copy Commits with cherry-pick


(feature) $ git commit -m "Fix typo"
> [feature d6b849c] Fix typo


(feature) $ git checkout master
(master) $ git cherry-pick d6b849c
> [master 288c050] Fix typo

The hashes will always be different because the committer timestamp (and perhaps the commiter name) are different.

Stash Changes


(feature*) $ git stash
(feature) $ git checkout master
(master) $ git stash pop


(feature) $ git stash show  # what-all do I have stashed?


(feature) $ git stash --keep-index  # leave everything that's going in to the next commit


(feature) $ git stash --include-untracked

Show Only Unmerged Commits


(feature) $ git log HEAD ^master  # show every commit in feature that's not in master

Note: git log == git log HEAD, but git log ^master won't show any commits.

Everything I've Learned About Gitin the Last Year

(So You Don't Have To)

The Theme of This Talk

The Theme of This Talk

Git Wants You to Fight It

But You Can Be Friends!

How?

Setting Up

Install the Latest

Git-ify Your Shell Prompt

Set Your Editor

Use Your Freedom of Choice

Get a Git Gutter

Run (Some) Git Commands

Configuring Git

Example: Setting Your Name and Email

Example: Adding a Global Gitignore

Example: Setting an Alias

History of Git

Version Control for Linux

First Commit

Totally Distributed

Git vs. Mercurial

Why Git Won

So…What is Git?

It's All About the Commits

One Hash Unlocks the Entire Universe!

Can't Hashes Conflict?

What's a Branch?

Huh! Then What's a Tag?

Why Use Branches?

What is the HEAD?

Moving the HEAD

Checkout vs. Reset

Pointers are Hard!

Staging and Committing

A Tale of Two Directories

Make New Commits, But Keep The Old

All the World's Staged

You Only Live Once

Unstaging

What Have I Done?

Pro Tip: Verbose Commit

Communicating with Remotes

Managing Remotes

Tracking Branches

Pull vs. Fetch

My Favorite Aliases

What's a Merge, Really?

The Simple Case

The Simple Case, Redux

The Complicated Case

Two Parents!?

The Wrong Way To Log

The Pretty Way To Log

The Right Way To Log

Enter Rebase

Rewriting History

The Awesomest Git Command Ever

Pro Tip: Rebase on Pull

More Tools

Fix Your Last Commit

Track Down Bugs with Bisect

Copy Commits with cherry-pick

Stash Changes

Show Only Unmerged Commits

More Resources

What About GitHub!?

You Are All Beautiful In Your Own Way

Thanks for listening!

Everything I've Learned About Git
in the Last Year