Thinking in Git

http://www.craftychild.com/finger-painting.htmlhttp://pixabay.com/en/cherry-sweet-cherry-red-fruit-167341/
Thinking in Git
Thinking in Git — Thinking in Git documentation http://talks.edunham.net/gwo2016/git/slides/#1
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Hi
Emily Dunham
edunham on irc.freenode.net
edunham@edunham.net
@qedunham
talks.edunham.net/gwo2016/git
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Agenda
How to look at software
development
What's Git?
Essential Git concepts &
commands
GitHub
Demo!
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Thinking about Software Development
Changing files
Some changes manual, other changes automatic
Changes for different reasons
Add feature, fix bug, test idea
Sometimes have several reasons at once, want
changes separate
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Why version control?
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How do you track changes?
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Goals of Distributed Version Control
Get the same file out that you put in
Work in parallel with others
Recombine individual work into one
project
Track and quantify changes over time
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Using Git
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Setting Up
Tell Git who you are:
$ git config --global user.name "John Doe"
$ git config --global user.email johndoe@example.com
You'll need SSH keys later
ssh-keygen -t rsa -b 2048, or
ssh-keygen -t ecdsa
Install Git (also tk and tcl if you want the GUI)
Set preferred editor
export GIT_EDITOR=vim in ~/.bashrc or
equivalent
Pick a project to work on
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Imagine...
You can time travel through the history of any
project!
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What's a repository?
Database of snapshots of your code
Universe whose history you can travel through
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Getting a repo
$ git init # Make a brand new repo
$ git clone <git clone url> # Start with a copy of another
# git@github.com:organization/reponame.git
# https://github.com/organization/reponame.git
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Looking at a repo
$ ls .git/
$ 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
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Undo repository creation
Warning
This deletes your history. Only do it if you really want to
stop having a Git repo here.
$ rm -rf .git
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Imagine...
What if you had to publish every change as soon as
you made it?
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How Git sees your project
Unstaged | Staged | Committed
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Imagine...
You decide exactly where time travelers are allowed
to land.
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What're staged changes?
Think "backstage", changes "waiting in the wings"
Files or parts of files can be added or removed
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Staging changes
$ echo "hello Great Wide Open" > foo
$ git add foo
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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)
bar
$ git commit --dry-run
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Undo?
Keeping uncommitted changes
$ git rm --cached foo
Go back to the latest committed version
$ git reset HEAD foo
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Imagine...
Time travelers get some signs and instructions when
they arrive
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Thinking about snapshots
Changes to a file plus pointers to
unchanged files
Each snapshot knows the state of all
tracked files
More efficient than just copying
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What's a commit?
snapshot of changes, author, date, committer (can differ
from author), parent commit
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Making a commit
$ git commit
$ man git-commit
-a, --all
-i, --interactive
--reset-author
--date=<date> (see DATE FORMATS in man page)
--allow-empty
--amend
-o, --only
-S, --gpg-sign
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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?
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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
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Undo?
# 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>
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Imagine...
Time travelers get a list of especially interesting
locations to visit
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What's a tag?
Marker attached to a
specific commit
Typically used for version or
release number
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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
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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>
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Undo?
$ git tag -d <tagname>
# And remove it from a remote repo
$ git push origin :refs/tags/<tagname>
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Imagine...
You can work on separate sets of changes that don't
affect each other
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What's a branch?
A parallel path of development, starting from a commit
that's in the tree
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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>
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Looking at branches
$ git branch
$ git show <branchname>
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Undo?
# 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>
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Imagine...
Someone else could work on the same repo in a
parallel universe
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What's a remote?
Another clone of more or less the
same repo
(remember when we cloned to get a
copy?)
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Adding a Remote
$ man git-remote
$ git remote add <name> <url>
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Looking at Remotes
$ git config -e
# OR
$ git remote show <name>
From one of my git configs...
[remote "origin"]
url = git@github.com:monte-language/monte.git
fetch = +refs/heads/*:refs/remotes/origin/*
[remote "edunham"]
url = git@github.com:edunham/monte.git
fetch = +refs/heads/*:refs/remotes/edunham/*
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Undo?
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>
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What's a merge?
Brings changes from one branch to another
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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")
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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.
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Looking at Merges
$ git diff <commit before> <merge commit>
# before merging, see changes
$ git log ..otherbranch
$ git diff ...otherbranch
$ gitk ...otherbranch
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Undo?
$ git merge abort
$ git reset --keep HEAD@{1}
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What's a rebase?
Changing history. Means others will have to force pull.
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Rebasing
$ git rebase -i <commit range>
HEAD~4
# last 4 commits
# Oops I forgot to pull
$ git pull --rebase
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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.
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Undo?
I should never have done that
$ git reset --hard ORIG_HEAD
I'm stuck in a broken rebase, get me out
$ git rebase --abort
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GitHub
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Not Exactly Git
Less distributed paradigm
Git never told us who to trust
Git doesn't care who you are
Watch Linus's talk for more detail
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Getting Started
https://github.com/join
Use the same email as your git config
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HTTP vs SSH Clones
Permission denied (publickey).
fatal: Could not read from remote
repository.
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
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Forking
Parallel repos (or possibly divergent)
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Pull Requests
Formalizes "Hi, please merge my changes"
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Annoying Tricks
Branches keep adding their content to PRs
Group management and access rights
No project license required
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Extra Features
Wiki
Gist
Issue trackers
Graphs
Repo descriptions and automatic README display
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Additional GitHub tricks
.github/CONTRIBUTING.md
.github/ISSUE_TEMPLATE.md
.github/PULL_REQUEST_TEMPLATE.md
README
Display test results on PRs
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Continuous Integration
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Playing Well With Others
Change history locally, never globally
Never force push (unless you have to)
Focused commits with clear commit messages
Follow project standards for branching, tagging, etc.
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Questions?
Emily Dunham
edunham on irc.freenode.net
edunham@edunham.net
@qedunham
talks.edunham.net/gwo2016/git
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Other Stuff
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checkout
$ git checkout branch
point HEAD at the tip of the specified branch
$ git checkout <revision> file
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gitrevisions
$ man gitrevisions
Commit hash
Refname
HEAD^n is nth parent of tip of current branch
branchname~n is nth generation ancestor of that
branch
Regex on commit message * :/broken
revision:path
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git bisect
Binary Search:
git bisect start
git bisect bad <commit>
git bisect good <commit>
git bisect next
git bisect reset <commit>
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git cherry-pick
$ git checkout <branch that needs special commit>
$ git cherry-pick <special commit from another branch>
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git format-patch
$ git format-patch origin/master
0001-first-commit.patch
0002-second-commit.patch
# I wonder what this patch does
$ git apply --stat 0001-first-commit.patch
# Let's merge!
$ git apply 0001-first-commit.patch
# Does your project use signed-off-by?
$ git am --signoff < 0001-first-commit.patch
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