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

[email protected]

@qedunham

talks.edunham.net/gwo2016/git


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Agenda

How to look at softwaredevelopment

What's Git?

Essential Git concepts &commands

GitHub

Demo!


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Thinking about Software Development

Changing filesSome changes manual, other changes automatic

Changes for different reasonsAdd feature, fix bug, test idea

Sometimes have several reasons at once, wantchanges 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 oneproject

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 [email protected]

You'll need SSH keys laterssh-keygen -t rsa -b 2048, or

ssh-keygen -t ecdsa

Install Git (also tk and tcl if you want the GUI)

Set preferred editorexport GIT_EDITOR=vim in ~/.bashrc orequivalent

Pick a project to work on


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Imagine...You can time travel through the history of anyproject!


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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

# [email protected]:organization/reponame.git# https://github.com/organization/reponame.git


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Looking at a repo

$ ls .git/

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

$ git showfatal: 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 tostop having a Git repo here.

$ rm -rf .git


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Imagine...What if you had to publish every change as soon asyou made it?


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How Git sees your projectUnstaged | Staged | Committed


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Imagine...

You decide exactly where time travelers are allowedto 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 statusOn 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 whenthey arrive


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Thinking about snapshots

Changes to a file plus pointers tounchanged files

Each snapshot knows the state of alltracked files

More efficient than just copying


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What's a commit?snapshot of changes, author, date, committer (can differfrom 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 interestinglocations to visit


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What's a tag?

Marker attached to aspecific commit

Typically used for version orrelease 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 oflatest 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'taffect each other


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What's a branch?

A parallel path of development, starting from a committhat'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 aparallel universe


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What's a remote?

Another clone of more or less thesame repo

(remember when we cloned to get acopy?)


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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 = [email protected]:monte-language/monte.gitfetch = +refs/heads/*:refs/remotes/origin/*

[remote "edunham"]url = [email protected]:edunham/monte.gitfetch = +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

<<<<<<< HEADThis 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, thencommit.

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 remoterepository.

Please make sure you have thecorrect access rights and therepository 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 globallyNever 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

[email protected]

@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

RefnameHEAD^n is nth parent of tip of current branch

branchname~n is nth generation ancestor of thatbranch

Regex on commit message * :/broken

revision:path


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git bisect

Binary Search:

git bisect startgit bisect bad <commit>git bisect good <commit>git bisect nextgit 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/master0001-first-commit.patch0002-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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Thinking in Git

Technology

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