Git Notes

GitLondon Notes – Scott Chacon and Charlie Smurthwaite

Help
git help [command]
git [command] —help

Remote management
git remote

Show what is staged (what am I going to commit?):
git diff —staged or —cached

Add all modified files:
git add -u

Stage and commit all modified files:
git commit -u
got commit -a

Interactive add:
git add -i

has a patch command that allows you to stage hunks of files

add -p

~/.gitconfig

git config alias — alias commands that will get stored in .gitconfig

git config —list

Unstage
git status shows command
git reset HEAD

LOGS

Forward forever (things I’m about to commit): git log origin/master..
Back forever: git log ..origin/master

BRANCHES

git branch

Default branch name is ‘master’: any name can be used

HEAD – Different to subversion. Means the branch you’re currently on. The branch that new commits will go to.

Make a new branch: git branch experiment
Switch to branch: git checkout experiment — changes HEAD and updates files in working directory to reflect branch
Commit: git commit — will move HEAD forward for this branch

Show remote branches: git branch -r
Show all: git branch -a
Show last commit on everyone’s branch: git branch -v

Range Forever: ..origin/master or origin/master.. (forward, backward) — equivalent to origin/master..HEAD

git checkout b - creates a new branch and switches to it

Can’t switch branches when there’s dirty files unless they can be merged

What is a branch? find .git/refs — show the heads — all branching does is writes SHA hash into these files

Branches usually change or get removed — i.e., a branch for each release

TAGs

Useful for fixing a branch in time: i.e., a particular version of a project so people can be sure it’s the right one in the future.

Technically the same as a branch but doesn’t move.

MERGING

Merge branch into master: git checkout master ; git merge experiment

Common workflows: master branch is usually in production, a development branch might be used for development then merged into master when ready.

Use branches to work on long running projects that affect the entire project, whilst still working on the older code without upsetting it. Example: converting site to postgres from mysql, meanwhile working on the production version that’s still mysql.

MERGE CONFLICTS

git diff —merge
git mergetool

remote and local branches are identical to git

GIT STASH

Move current work onto a temporary stack of stashes: git stash
Makes working directory clean again so you can continue working on another branch
Good for work that isn’t ready to commit yet

git stash save
git stash list

Go back to the stash: git stash apply

GIT INTERNALS

Optimise local files: git gc
Similar to delta compression (i.e. svn), but each git version might have different algorithms
Writes binary packed files to store
Just a storage format rather than how git usually deals with files

git stash apply

INTERNALS: INTEGERITY

alex@alex ~/Documents/Code/furnish[master*]$ git-fsck
dangling blob 012e795be91e2be1945880455f4cdd631f4a313c

git show 012e795be91e2be1945880455f4cdd631f4a313c
git cat-file -p 012e795be91e2be1945880455f4cdd631f4a313c

ADVANCED

REVISION SELECTION

Ways to refer to revisions:

• full SHA1, partial (at least 4 characters and it’s not ambiguous)
• branch, remote or tag names
• caret parent – default^2 (2nd parent of default – up the tree)
• tilde parent – default~2 (parent of the parent — always the first parent of the branch)
• Combinations of the caret and tilde syntax
• Specify path within a spec: default:path/to/file
• Relative specs (within reflog, git reflog to show): master@{yesterday}
• Ranges: branch/master..SHA1 (or partial SHA1)
• Three dot ranges: Show common changes between SHA1…SHA1

Examples:

git reflog
git show HEAD@{3}:README

Show patch alongside log: git log -p
Visualise lots of commits: git log —pretty=oneline
Visualise lots of commits with branches in graphs: git log —pretty=oneline —graph

How do I make A look like B? git diff A B — not usually what you want, not what a merge would do
Instead, compare two branches or commits using: git diff A…B — compares against common ancestor — different to triple dot syntax in revision selection

ANNOTATION

view who changed the file: git blame file
Detect lines copied from other files: git blame -C file

git commit —amend

merging with rebase: git rebase — goes back to common ancestor, takes all commits, saves them as patch files, tries to reapply them to another branch. This makes the branch look like it’s got a linear history, because you can’t tell they’ve been merged after a rebase.

Rebase can make it easy to:

• change commit messages
• remove a large file that was accidentally added
• rebase -i is the interactive version

Generally useful to clear up your local commits before pushing to server, not a great idea to rebase after push.
(best at staging)

FILTER BRANCH

Nuclear option for changing entire history. Let people know the HEAD is changing and they need to rebase.

git filter-branch —tree-filter ‘rm -f filename’ HEAD

i.e. changing email address across entire history (—env-filter) – dangerous
works with ranges

CHERRY PICKING

git cherry-pick sha1

UNDO

single file: git checkout sha1/commit/HEAD file — there’s no undoing this undo
whole project: git reset -hard - changes staging, index and pointer

git branch will keep things how they are — you can always get back to it. (drops a pointer). This makes the following possible:

Let’s say you’ve made changes but want to put the master to how it was and branch off the new stuff:

git branch experiment
git reset —hard origin/master
git checkout experiment

By default, git reset changes the staging area.

BISECT

Find a commit if you have a way of searching for a yes/no value. Usually used to find where a bug was introduced. Moves the pointer around and lets you merge in the last known good state.

git bisect start
git bisect bad (HEAD is bad)
git bisect good (SHA1 of bad)
git bisect reset — stop

GIT CLEAN

git clean will remove untracked files

GIT PROTOCOLS

ssh
git clone alex@dev.helicoid.net:/absolute/path/File.git

http/s
push can work but it’s a lot of work (dav)
pull is nice, simple and uses low resources, expensive at the client side
needs git update-server-info

git
daemon
efficient for clients: server creates packfiles for each client

INSTALLING ON OUR SERVER

1. server needs git
2. git —bare init
3. mkdir Tiktrac.git
4. (locally) git init
5. git remote add helicoid alex@dev.helicoid.net:/usr/share/git/Tiktrac.git (will prompt for passwords if no key is set up)
6. git push helicoid

gitosis makes this easier (could work with ldap)

tortoise-git for Windows

TextMate git

GARBAGE COLLECTION

git gc -auto - check to see if there are too many loose objects

gc.aggressiveWindow — useful after subversion import to reduce the size

RECOVERY

git branch D branch_name - deletes branch
Finding it again: Figure out what the SHA was. Try git reflog (before it gets GC’d)

git fsck —lost-found
puts dangling trees and blobs in lost-found
really needs a script to find them

BEST PRACTICES

develop integrate
using lots of branches – before you start doing anything unusual, or a risky merge, start a branch
topic branches –
long commit messages – style for company or open source project, passive voice, non-english users for open source – summarise on first line because some sites or tools only show first line
commit often (not necessarily push)
push when it seems ok to share (if you want to share a lot maybe push to a remote branch)
talk to people: explain why you created remote branches
tools, protocol, structure: decided on within the company

difference between version control and backups — some companies would need to make it company policy to do local backups, or use multiple remotes so developers can have their own remotes

HOOKS

local
server-side: per-receive, post-receive, update, post-update

return 0 will halt commit – this could be tied to your commits

INTERFACE STUFF

Colour in UI:
git config —global color.diff auto
git config —global color.status auto
git config —global color.branch auto

Bash prompt:
http://gist.github.com/31631

Web view:
git instaweb -d webrick