Thinking in Git


Permanent link to these slides:


Why listen to me?

  • 5 years at OSL
  • ran bootcamp, LUG
  • Taught a lot of newbies this stuff

"Git is the most popular source code management and version control system in the open source community. Its complexity and power make it the best choice for most projects, while simultaneously giving it a daunting learning curve for newcomers. This talk will assume no background knowledge of version control, and will teach the basics of Git in order to give you an accurate mental model of what the tool does, and help you fix mistakes then ask the right questions if you run into problems using it later."




You won't memorize all the commands in an hour but this will help you ask the right questions

Thinking about Software Development


Why version control?


TODO: pic of directory listing here instead


Types of version control


Goals of Distributed Version Control



reliability means put one file in, get same file out again, guaranteed. spell out Single Point of Failure.

Git's buzzwords



We'll get to branches later... but you've noticed people saying oddly horticultural things like branches and trunks

How Git sees your project


Unstaged | Staged | Committed


Using Git


We're going to talk about a lot of commands now.

Don't be afraid. Don't expect to know everything at first.

These slides will be online; the link will show up again at the end.

Setting Up


ECDSA is the new hotness -- elliptic-curve digital signature algorithm -- much smaller keys have comparable security

  • GitHub can handle ECDSA, GitLab only does RSA as of 5.1.0

What's a repository?


Database of snapshots of your code

$ ls .git/

Getting a repo

$ git init

$ git clone <git clone url>


Looking at a repo

$ git show
fatal: bad default revision 'HEAD'
# To be expected with nothing in the repo

$ git show
fatal: Not a git repository (or any of the
       parent directories): .git
# not in a repo

$ git log



This deletes your history. Only do it if you really want to stop having a Git repo here.
$ rm -rf .git

What're staged changes?


Staging changes

$ touch foo
$ git add foo

Looking at staged changes

$ touch bar
$ git status
On branch master

Initial commit

Changes to be committed:
  (use "git rm --cached <file>..."
   to unstage)
    new file:   foo
    Untracked files:
      (use "git add <file>..." to include
       in what will be committed)
$ git commit --dry-run


$ git rm --cached foo
$ git reset HEAD foo


next, snapshots

Thinking about snapshots



next, commits

What's a commit?

Snapshot of changes

Includes snapshot (with pointers to unchanged files), author, date, committer (can differ from author), parent commit


Making a commit

$ git commit
$ man git-commit
-a, --all
-i, --interactive
--date=<date> (see DATE FORMATS in man page)
-o, --only
-S, --gpg-sign


-o is for only files from command line disregarding the stash Specifying file names disregards staged changes, plus stages all current contents

Looking at commits

# details on latest or specified
$ git show

# Summary of recent, or a range
$ git log

$ man gitrevisions # ranges

What about commits per file?

$ git blame <file>

Commit display options

$ git show

$ git show --oneline

# see PRETTY FORMATS section of
$ man git-show

# Check the GPG signature
$ git show --show-signature

# Want a GUI?
$ gitk


# just one file
$ git checkout <commit> <filename>
$ git add <filename>
$ git commit -m "i put that file back how it was"

Or undo the whole commit

$ git revert <commit to revert to>


next: remotes Reverting makes a revert commit. Reversability > hiding mistakes

What's a remote?


Another clone of more or less the same repo

(remember when we cloned to get a copy?)


Adding a Remote

$ man git-remote

$ git remote add <name> <url>


Looking at Remotes

$ git config -e

# OR

$ git remote show <name>

From one of my git configs...

[remote "origin"]
  url =
  fetch = +refs/heads/*:refs/remotes/origin/*
[remote "ed"]
  url =
  fetch = +refs/heads/*:refs/remotes/ed/*


Do you prefer text editor...

$ git config -e
# delete or change remote

... or commands?

$ man git-remote
$ git remote rename <old> <new>
$ git remote remove <name>


"Undoing" push to remote is... trickier next: tags

What's a tag?


Adding a Tag

$ man git-tag
$ git tag -m <msg> <tagname>

Default is lightweight tag -- just a reference for SHA-1 of latest commit

Pass -s or -u <key-id> to GPG-sign

Looking at Tags

# List all available tags
$ git tag

# List tags matching regex
$ git tag -l 'regex'

# I want this version!
$ git checkout <tag name>


$ git tag -d <tagname>

# And remove it from a remote repo
$ git push origin :refs/tags/<tagname>

What's a branch?


A parallel path of development, starting from a commit that's in the tree


Point out why the arrows are "backwards"

Making a branch

# track remote branch by default if one matches
$ git checkout -b <branchname>

# Shorthand for:
$ git branch <branchname>   # create
$ git checkout <branchname> # check out

# Pushing a branch to a remote
$ git push <remotename> <branchname>

Looking at branches

$ git branch

$ git show <branchname>



GitHub's "network" graph and gitk are good for this


# delete only if fully merged
$ git branch -d

# Delete, I Don't care what I lose
$ git branch -D

# delete remote branch
$ git push <remotename> :<branchname>

What's a merge?



that joke about how a group of developers is called a merge conflict

Making a Merge

# Branch you're changing
$ git checkout mywork

$ git merge master

# Merge conflicts?
$ git status
    On branch mywork
    You have unmerged paths.
      (fix conflicts and run "git commit")



Merge Conflicts

<<<<<<< HEAD
This content was in mywork but not master
This content was in master but not mywork
>>>>>>> master

Replace all that stuff with what the content should be.

git add the file.

Check that you've got everything with git status, then commit.

Or consider git mergetool for an interactive option.

Looking at Merges

$ git diff <commit before> <merge commit>

# before merging, see changes
$ git log ..otherbranch
$ git diff ...otherbranch
$ gitk ...otherbranch


$ git merge abort
$ git reset --keep HEAD@{1}

What's a rebase?


Changing history. Means others will have to force pull.


Don't do this unless you know what you're doing... But here's how to know what you're doing.


$ git rebase -i <commit range>
                # last 4 commits

# Oops I forgot to pull
$ git pull --rebase

Looking at the rebase

# Rebase 1a20f51..147c812 onto 1a20f51
# 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.


Make sure you have your git editor set!


I should never have done that

$ git reset --hard ORIG_HEAD

I'm stuck in a broken rebase, get me out

$ git rebase --abort

GitHub Stuff


Not Exactly Git


Watch Linus's talk for more detail

HTTP vs SSH Clones

Permission denied (publickey).
fatal: Could not read from remote

Please make sure you have the
correct access rights and the
repository exists.

HTTP clone prompts for username and password

SSH clone uses key from your account



Pull Requests


Annoying Tricks


Extra Features

Continuous Integration


Playing Well With Others



Permanent link to these slides:

Other Stuff


$ git checkout branch

point HEAD at the tip of the specified branch

$ git checkout <revision> file


$ man gitrevisions

git bisect

Binary Search:

git bisect start
git bisect bad <commit>
git bisect good <commit>
git bisect next
git bisect reset <commit>

git cherry-pick

$ git checkout <branch that needs special commit>
$ git cherry-pick <special commit from another branch>