Advanced Git let talk

@skalnik i’m

a few of my favorite things Raindrops on roses and whiskers on kittens… Just kidding, I love git.

merge conflicts

# Merge a branch $ git merge conflict you can do this after you run `merge-conflict.sh`: https://gist.github.com/skalnik/4951428

Auto-merging greeting.txt CONFLICT (content): Merge Automatic merge failed; fi Oh god wtf just happened. Lets check out greeting.txt

<<<<<<< HEAD Yay! DevconTLV! ======= DevconTLV Woo! >>>>>>> conflict WHAT IS GOING ON HERE?! Top is what was on HEAD (for us, master) Bottom is what was on the conflict branch Lets get rid of the extra stuff and commit!

rerere

remembers merge conflicts

# It’s gotta be enabled $ git config --global \ rerere.enabled 1 Resets our HEAD, working copy, & index --soft does only HEAD --mixed (default) resets the index, but not working copy

a32 2e2 8b3 fe1 2bd topic master Lets say you have a topic branch, and you’ve modified some of the same lines as master

a32 2e2 8b3 fe1 2bd topic master af3 when you merge master in, you’ll have to resolve the conflict

a32 2e2 8b3 fe1 2bd topic master af3 e69 d19 f4a 3a1 However, a long lived topic branch may do this many times. If any of you read the Linux kernel mailing list, you may remember Linus complaining about these “useless merges” when a subsystem maintainer asked him to pull a branch. So if we got rid of these as we made them

a32 2e2 8b3 fe1 2bd topic master f3c e69 d19 f4a 3a1 So if we get rid of these, great! But once we merge master back in… rerere to the rescue!

rebase

rebase is not a merge

rebase is preparation for a merge

merge makes a multi-parent commit

rebase reorders commits before your branch

rebase simulates people taking turns working

# Rebase interactively over # last 5 commits $ git rebase --interactive \ HEAD~5

a32 2e2 8b3 e69 d19 You can delete commits

a32 2e2 e69 d19 Changing any parent changes the children

a32 2e2 73e 1d9 Or pull them out

a32 2e2 e69 d19 And reorder them

a32 d19 e69 2e2 Normally these SHAs would change, but so you can see that they swap, I’ll leave them

a32 d19 41a 2e2 Or even take the last 2 commits, and squash ‘em together

a32 d19 e69 2e2 + a3f =

a32 d19 a3f Or even amend them

a32 fa1 df4 Or even completely edit them Talk about git commit --amend

# Rebase interactively and # autosquash last 5 commits $ git rebase -i --autosquash \ HEAD~5 fixup! squash! These are automatically set to fixup/squash when rebasing interactively then

stash

a super quick branch

local only

stack based push pop peek

# stash your changes $ git stash

# save ‘em $ git stash save ‘message’

# list ‘em $ git stash list

# use ‘em $ git stash pop

# use a specific one $ git stash pop stash@{1}

# or if you want to keep it $ git stash apply

# or if you want to keep it $ git stash apply

# too good to just stash? $ git stash branch

cherry-pick

“cherry picking” a commit into your branch

# All you need is the SHA $ git cherry-pick Or multiple! This creates a brand new commit, but with the same diff It’s much like a manual rebase

# What if you don’t want # the commit? $ git cherry-pick --no-commit Or multiple! This creates a brand new commit, but with the same diff It’s much like a manual rebase

ref log

a journal of your local actions

2a52e96 HEAD@{0}: commit (merge): Merge branches 'feature_division_ 369adba HEAD@{1}: checkout: moving from feature_subtraction_polishe 818f033 HEAD@{2}: checkout: moving from feature_division_polished t 57d0bf6 HEAD@{3}: commit: Removing subtraction from the division li cb2d322 HEAD@{4}: checkout: moving from feature_division to feature e650f37 HEAD@{5}: checkout: moving from master to feature_division 369adba HEAD@{6}: checkout: moving from feature_division to master e650f37 HEAD@{7}: rebase -i (continue): Fixed a typo in a tested va 3c9306f HEAD@{8}: cherry-pick 09b08e4 HEAD@{9}: checkout: moving from feature_division to 09b08e4 9fc18b5 HEAD@{10}: checkout: moving from feature_division to 9fc18b 9fc18b5 HEAD@{11}: commit: Fixed a typo in a tested value of divisi d5ef5f0 HEAD@{12}: checkout: moving from feature_division_polished cb2d322 HEAD@{13}: commit (amend): Added subtract feature 6a795b8 HEAD@{14}: rebase: Added subtract feture 369adba HEAD@{15}: checkout: moving from feature_division_polished d5ef5f0 HEAD@{16}: checkout: moving from master to feature_division 369adba HEAD@{17}: checkout: moving from feature_division_polished d5ef5f0 HEAD@{18}: checkout: moving from feature_division to featur d5ef5f0 HEAD@{19}: checkout: moving from feature_division_polished d5ef5f0 HEAD@{20}: checkout: moving from d5ef5f0e74c56bd678ea1d504c d5ef5f0 HEAD@{21}: checkout: moving from 818f033c4ae7f26b2b29e90494

# We messed up good $ git reset --hard HEAD@{3} Resets our HEAD, working copy, & index --soft does only HEAD --mixed (default) resets the index, but not working copy

hunks

# Hunk level adding, i.e. # patch mode $ git add --patch

diff --git a/app.coffee b/app.coffee index c99027a..b1e7e9b 100755 --- a/app.coffee +++ b/app.coffee @@ -10,11 +10,7 @@ app.configure -> app.use express.methodOverride() app.use app.router -app.configure 'development', -> - app.use express.errorHandler({ dumpExceptions: true, showStack: true }) - -app.configure 'production', -> - app.use express.errorHandler() +app.use express.errorHandler() port = process.env.PORT || 3000 Stage this hunk [y,n,q,a,d,/,e,?]? y - yes n - no s - split e - open in $EDITOR

Stage this hunk [y,n,a,d,/,j,J,g,e,?]? ? y - stage this hunk n - do not stage this hunk a - stage this and all the remaining hunks in the file d - do not stage this hunk nor any of the remaining hunks in the file g - select a hunk to go to / - search for a hunk matching the given regex j - leave this hunk undecided, see next undecided hunk J - leave this hunk undecided, see next hunk k - leave this hunk undecided, see previous undecided hunk K - leave this hunk undecided, see previous hunk s - split the current hunk into smaller hunks e - manually edit the current hunk ? - print help

# But that’s not all! $ git reset -p

# Checkouts too! $ git checkout -p

hub

hub introduces git to GitHub

# Install via Homebrew $ brew install hub # or with curl $ curl \ http://defunkt.io/hub/standalone \ -sLo ~/bin/hub && \ chmod +x ~/bin/hub

# Clone a GitHub repo $ git clone user/repo # vs $ git clone \ git://github.com/user/repo

# Private repo? $ git clone -p github/github

# Fork current repo $ git fork

# Then after some changes $ git pull-request

plumbing

git is a key-value store

# Get the object ID $ git hash-object $ echo “Yay DevconTLV” | git hash-object -w --stdin 053a0094e47bd27c88ee17e205f42beb974791aa $ find .git/objects -type f .git/objects/05/3a0094e47bd27c88ee17e205f42beb974791aa

# Look at a git object $ git cat-file $ git cat-file -p 053a0094e47bd27c88ee17e205f42beb974791aa Yay DevconTLV $ git cat-file -t 053a0094e47bd27c88ee17e205f42beb974791aa blob

Lets talk trees! hash-object makes blobs for us. But those are just content. How does git keep track of multiple files? And file names?

# Update the staging area $ git update-index To write a tree, we must first create the index, or staging area. $ git update-index --add --cacheinfo 100644 \ 053a0094e47bd27c88ee17e205f42beb974791aa greeting.txt $ git status (shows greeting.txt)

# Ignore a file $ git update-index \ --assume-unchanged \ Cool aside,

# Write the index tree $ git write-tree This simply takes the current index and writes it as a tree, and gives back the ID $ git write-tree 202ad037ef5d9a7b369eb4a56fb5fcb3a4c74228

# Commit an existing tree $ git commit-tree Now that we have a tree, we can commit it! $ echo “Initial commit!” | git commit-tree 202ad037ef5d9a7b369eb4a56fb5fcb3a4c74228 7847536f3db84e7b21ef79427f8ec7ddb4abdc99 Pass it -p for a parent $ echo 'Woo! DevconTLV!' > greeting.txt $ git hash-object -w greeting.txt 989932c6ebee1b4a284e8a47a1eb9095e971a599 $ git update-index --add --cacheinfo 100644 989932c6ebee1b4a284e8a47a1eb9095e971a599 greeting.txt $ git write-tree 54e49d1aaff28b88c6639b1b4634f6bde673b39d $ echo "Commit #2" | git commit-tree 54e49d -p 784753 2b63f9dffeb0b40e34a491890ae35241b34e360e

# Lets update the master ref $ echo “SHA” > \ .git/objects/refs/heads/master $ echo “2b63f9dffeb0b40e34a491890ae35241b34e360e” > .git/objects/refs/heads/master $ git log --stat

fin

any questions?