How to Really GetHow to Really GetGitGit

Sunday, February 8, 2015Susan Tan

@ArcTanSusan

Who am I?

Software Engineer @Piston who uses Python and gitA New-Yorker-who-moved-to-San-FranciscoAlso Piston is .hiring

I. Git SetupI. Git Setup

Git Configs: AliasesGit Configs: Aliases

[alias] st = status ci = commit br = branch co = checkout df = diff lg = log -p

$ git st# On branch master# Untracked files:# (use "git add <file>..." to include in what will be committed)## _posts/2009-02-06-helpful-command-aliases.textilenothing added to commit but untracked files present (use "git add" to track)

In ~/.gitconfig, put this here:

Git Configs: ColorsGit Configs: Colors

[color "status"] added = magenta changed = yellow untracked = cyan

In ~/.gitconfig, put this:

Git Configs:Git Configs:

Tab AutocompletionTab Autocompletion1. Follow instructions for your OS.2. Then you can use auto tab completion on long commands

here

$ git chec<tab>

Git Configs:Git Configs:

A Useful Bash PromptA Useful Bash Prompt

https://github.com/bobthecow/git-flow-completion/wiki/Install-Bash-git-completion

A useful prompt shows

current branchcurrent directorycurrent virtualenvstatus of working directory

Who is this talk for?You already know the basics of git, but you still makemistakes (well, so does everyone)

Common git commands you already know:git addgit status git push origingit fetch origin

You want to know how to deal with mistakesCommon git commands you'll learn about:

git rebasegit resetgit refloggit revert

This Should Look FamiliarThis Should Look Familiar

Source: http://git-scm.com/book/ch1-3.html

This should be familiar, tooThis should be familiar, too

This may be familiar, tooThis may be familiar, too

This should be familiar, too -- Collaboration with git.This should be familiar, too -- Collaboration with git.

Source: http://nvie.com/posts/a-successful-git-branching-model/

II. Mistakes and howII. Mistakes and howto fix themto fix them

"People think computers will keep them from making mistakes.They're wrong. With computers you make mistakes faster."--Adam Osborn

Source: http://justinhileman.info/article/git-pretty/git-pretty.pdf

git rebasegit rebaseWhy use rebase?

1. git rebase to keep a branch updated

2. git rebase --interactive flag to change history

git rebase: The Simplest Usagegit rebase: The Simplest Usage

Note: "master" here means remote upstream's master branch.

git rebase: The Simplest Usagegit rebase: The Simplest Usage

What if your personal branch "develop" needs to rebaseWhat if your personal branch "develop" needs to rebase

against a feature branch shared by your team members?against a feature branch shared by your team members?

Note: "master" here means remote upstream repo's master branch.

What if your personal branch "develop" needs to rebaseWhat if your personal branch "develop" needs to rebase

against a feature branch shared by your team members?against a feature branch shared by your team members?

Note: "master" here means remote upstream repo's master branch.

git rebase master/feature develop

git rebase --onto master feature develop

Note: "master" here means remote upstream repo's master branch.

OR

git rebasegit rebase

git rebase <remote_repo>/<remote_branch> <your_branch_name>

git rebase --onto <first_this> <then_this> <last>

Syntax for git rebase

What if the feature branch needs to rebase against aWhat if the feature branch needs to rebase against a

upstream repo's master branch shared by everyone?upstream repo's master branch shared by everyone?

Note: "master" here means remote upstream repo's master branch.

What if the feature branch needs to rebase against aWhat if the feature branch needs to rebase against a

upstream repo's master branch shared by everyone?upstream repo's master branch shared by everyone?

Note: "master" here means remote upstream repo's master branch.

Rebase ConflictsRebase Conflicts

Rebase Conflicts require manual fixesRebase Conflicts require manual fixes(because git isn't clever enough to fix conflicts)

1. Locate conflict markers (<<<<<<) andmake edits to resolve

2. Resolve a conflict in each file with gitadd <filename>

3. git rebase --continue4. Alternatively, you can undo the git

rebase with git rebase --abort

Fixing git rebase conflicts is notFixing git rebase conflicts is notalways the right solutionalways the right solutiongit checkout mastergit branch -D featuregit fetch mastergit checkout -b feature master/featuregit checkout -b develop_v2git merge develop_v1git branch -D develop_v1

git fetch mastergit checkout [YOUR BRANCH]git rebase --onto master/feature [commit]

OR

Different computers, sameDifferent computers, samebranchbranch

git fetch origin && git rebase origin/<MY_BRANCH>

Note: "origin" is your personal cloned copy of an upstream masterrepo

git pull --rebase

Or, equivalently

git rebase --interactive <HASH> orgit rebase --interactive HEAD^

Defn: To re-order, edit, squash, or remove manycommits at once

git rebase -i HEAD~5

Squashing commitsSquashing commits

git resetgit reset

Defn: Reset current HEAD to the specified state

git reset --soft HEAD^

Defn: Set files from previous commit onto staging area. HEADpoints to the previous commit. This leaves all your changed filesas "Changes to be committed".

git reset --soft HEAD^

git reset --hard HEAD^

Defn: Abandon everything since your last commit. HEAD pointsto the previous commit. Nothing is in staging. Use with greatcaution

git refloggit reflog

Defn: shows all the commits and actions on your machine that hasever happened such as branch switches, rebases, resets, branchdeletions, cherry-picks, reverts.

git reflog git reflog --grep="Revert"

How to make git reflog more usefulHow to make git reflog more useful

git reflog --all --date=iso

You can undo a hard reset with the help of git reflogYou can undo a hard reset with the help of git reflog

git reset --hard HEAD^^ to remove the last 3 commits

You can undo a hard reset with git reflog + git reset --hardYou can undo a hard reset with git reflog + git reset --hard

git reset --hard a64b0f2 to restore branch to previous stategit reset --hard a64b0f2 to restore branch to previous state

Why use git reflog?Why use git reflog?

You lost commits when you did a git reset --hardYou squashed too many commits into 1 commit, so youwant to undo git rebase -iYou accidentally deleted branches and want to restorethem

Summary: Use reflog to look up old lost commits

Use cases for git reflogUse cases for git reflogLook up a commit hash. Then either

create a new (un-named) branch out of this commitgit checkout -b <COMMIT_HASH>

reset your branch to a previous stategit reset --hard <COMMIT_HASH>git reset --soft <COMMIT_HASH>

cherrypick that lost commit on top of your branchgit cherry-pick <COMMIT_HASH>

How long does theHow long does theoutput of reflog last?output of reflog last?

Hanging commits are removed from the local repository bygarbage collection (gc) or by manual removal. Default is 30days.

[gc] reflogExpire = never reflogExpireUnreachable = never

git revert 638351801cd802d6e0c4e601db1eca801dd58936

Defn: Makes a revert commit with a message that states thespecified commit is reverted

git revert <HASH>

Defn: Revert changes specified by 4th last commit awayfrom HEAD and create a new commit with reverted changes.

git revert HEAD~3

git revert --continueContinue after resolving conflicts git revert --abortCancel operation and return to pre-sequence state git revert --quitCan be used to start over after a failed cherry-pick or revert

Git revert conflictsGit revert conflicts

When to use git reset vs. git revertWhen to use git reset vs. git revert

Permanent MistakesPermanent Mistakes

Permanent MistakesPermanent Mistakes

git push -f origin <REMOTE>

SummarySummaryIf you run into git problems, the solution is most likely touse one of these --

git rebasegit resetgit refloggit revert

III. Automate gitIII. Automate git

Problem: Repetitive branch deletingProblem: Repetitive branch deleting

vagrant@precise64:~/work/savage$ git push origin :73997184To git@github.com:onceuponatimeforever/savage.git - [deleted] 73997184vagrant@precise64:~/work/savage$ git push origin :76321732-on-masterTo git@github.com:onceuponatimeforever/savage.git - [deleted] 76321732-on-mastervagrant@precise64:~/work/savage$ git push origin :77910316 To git@github.com:onceuponatimeforever/savage.git - [deleted] 77910316vagrant@precise64:~/work/savage$ git push origin :77910316-bottleTo git@github.com:onceuponatimeforever/savage.git - [deleted] 77910316-bottlevagrant@precise64:~/work/savage$ git push origin :77910316-bottle-from-scratchTo git@github.com:onceuponatimeforever/savage.git - [deleted] 77910316-bottle-from-scratchvagrant@precise64:~/work/savage$ git push origin :2.0/master

IPython notebook supports gitIPython notebook supports git

Solution: IPython notebook scriptSolution: IPython notebook script

Problem: Fetch & rebase repetitionsProblem: Fetch & rebase repetitions

cd <PROJECT>git fetch upstreamgit rebase upstream/master

cd ../<ANOTHER_PROJECT>git fetch upstreamgit rebase upstream/master

# And again....

Solution: IPython notebook scriptSolution: IPython notebook scriptlist_of_projects = ['ipython', 'oh-mainline']

def update(project): %cd {project} !git checkout master !git fetch upstream !git rebase upstream/master !git push origin master %cd .. print "Done git rebasing this repoo: ", {project} for project in list_of_projects: update(list_of_projects[project]) print "---------------------------------"

Solution: IPython notebook scriptSolution: IPython notebook script

Thanks! Q&A Time.Thanks! Q&A Time.