Professional Practice: Git Seminar

Adapted from Nice Reidman's interactive Git tutorial

"Learn git concepts, not commands"

Resources

• Pro Git Book
• Introduction to GitHub course on GitLab
• This tutorial in more depth

Local Version Control

Centralised Version Control

Distributed Version Control

Git Overview

Getting a Remote Repository

• Fork https://github.com/john-french/git_training

  • creates your own remote copy of a repository

• Get your copy of the remote repo onto your machine

git clone https://github.com/{YOUR USERNAME}/git_training.git

• creates a new directory called git_training on your machine

Cloning a repository

Adding new things

• Move to the repo directory and add a new file

cd git_training
echo "This is Bob" > Bob.txt

• Check the status of your working directory and view changes

git status
git diff

Adding Changes

Adding Changes

• Add changes to the staging area

git add Bob.txt
git diff --staged

• Commit changes to the local repo

git commit -m "Added Bob"

• Push changes to the remote

git push

Commit Messages: Bad

Commit Messages: Good

$ git log --oneline -5 --author pwebb --before "Sat Aug 30 2014"
5ba3db6 Fix failing CompositePropertySourceTests
84564a0 Rework @PropertySource early parsing logic
e142fd1 Add tests for ImportSelector meta-data
887815f Update docbook dependency and generate epub
ac8326d Polish mockito usage

Branching

Branching

Branching

• Create a new branch called updateAlice

git branch updateAlice

• Switch to the branch we just created

git checkout updateAlice

• Switch back to master

git checkout master
git branch

Branching

• Undo and use a shortcut instead
• Delete branch updateAlice

git branch -d updateAlice

• Create and update branch in one go

git checkout -b updateAlice
git branch

Creating a branch

Checking out a branch

Making Changes on a Branch

• Make a change to Alice.txt by adding more text

echo "More content added" >> Alice.txt

• Add and commit this change

git add Alice.txt
git commit -m "Updated Alice"

• Push these changes to the remote repository

git push
fatal: The current branch updateAlice has no upstream branch.
To push the current branch and set the remote as upstream, use

    git push --set-upstream origin updateAlice

• List remote branches

git branch -a

Merging

Merging

Fast-Forward Merge

• When no new commits have been added to the base branch

3 Way Merge

• When new commits have been added to the base branch

Fast Forward Merge: Before

Fast Forward Merge: After

Fast Forward Merge

• See the Updated Alice in commit history on updateAlice branch

git log

• Checkout master, notice that commit isn't on the master branch

git checkout master
git log

• Merge the updateAlice branch into master

git merge updateAlice
git log

3 Way Merge: Before

3 Way Merge: After

3 Way Merge

• Create new branch

git branch newAlice

• Make changes on master

echo "Some more stuff" >> Bob.txt
git add Bob.txt
git commit -m "Updated Bob"

• Checkout newAlice branch and make changes there

git checkout newAlice
echo "Even more stuff" >> Alice.txt
git add Alice.txt
git commit -m "Updated Alice again"

3 Way Merge

• master and updateAlice have now diverged

• Switch back to master and merge newAlice

git checkout master
git merge newAlice

• Notice new merge commit Merge branch newAlice

git log --pretty=short
commit 5296df5d5e21747385eed68b1195b05dfce99cfc (HEAD -> master)
Merge: 0c34535 e849430
Author: John French <john.french@gmit.ie>

    Merge branch 'newAlice'

Merge Conflicts

• Create and checkout a new branch and make some changes on it

git checkout -b fixBob
echo "Hi! I'm Bob. I've been here for a while now." > Bob.txt
git add Bob.txt
git commit -m "Bob's here for a while"

• Checkout master and make changes to the same file

git checkout master
echo "Hi! I'm new here." > Bob.txt
git add Bob.txt
git commit -m "Bob's new here"

Merge Conflicts

• Merging fixBob won't work, files have conflicting changes

git merge fixBob
Auto-merging Bob.txt
CONFLICT (content): Merge conflict in Bob.txt
Automatic merge failed; fix conflicts and then commit the result.

• View contents of Bob.txt

cat Bob.txt
<<<<<<< HEAD
Hi! I'm new here.
=======
Hi! I'm Bob. I've been here for a while now.
>>>>>>> fixBob

Merge Conflicts

• Open file in text editor and fix conflict manually (or using a tool)
• Add and commit fixed file

git add Bob.txt
git commit

• Too messy! Cancel the merge

git merge --abort

Getting Remote Changes

Keeping your copy of the repository up-to-date

Fetch

Pull

Stashing

• Save work in progress that's not ready to commit

git stash

• List stashes

git stash list

• View a stash

git stash show

• Apply a stash (retrieve the changes)

git stash apply

Aliases

Creating Command Shortcuts

• Git aliases are command Shortcuts
  • use sparingly or you'll forget the real syntax

$ git config --global alias.co checkout
$ git config --global alias.ci commit

• Useful for longer commands

Useful Git Commands

• Keep notes of new commands you learn
• Build up a library of handy commands

My Command Library

Action	Git Syntax
List tags and commit ids	git show-ref --tags
Squash last 4 commits into one commit with new message	git reset --soft HEAD~4
Amend last commit message	git commit —amend
Force push to remote (overwrites history, Don't do this!)	git push -f origin
List tags	git tag -l
Check out tag	git checkout tags/<TAG>
Show history in format [short SHA1] [message]	git log --oneline
Show sha1, author and message of a single commit	git log --pretty=short -n 1 <SHA1>
Check if object is present in repo and return its type	git cat-file -t [SHA1]
Get last common ancestor of two branches	git merge-base branch1 branch2
Abort a merge	git merge --abort
Create a new branch and check it out	git checkout -b branch_name
List remotes	git remote -v
Show details of remote	git remote show remote_name
Delete branch from remote	git push origin :branch_name
Resolve all conflicting files below a directory with the remote side of the merge (use ours for the local side)	`grep -lr '<<<<' .
Resolve conflics in specific file/directory	git mergetool <file/directory>
Reset resolved merge conflict to conflicted state	git checkout -m <file>
Remove local branches no longer present on remote	git remote prune origin
Reset local repo to nth commit behind current HEAD	git reset --hard HEAD~n
Revert commit without committing	git revert -n <sha1>
Stage changes interactively	git add -p
Checkout previously checked-out branch	git checkout -
Search in git command history	CTRL-R
Check out file from another branch	git checkout <branch_name> -- <paths>
Cherry pick a merge commit, appending a line saying “cherry picked from commit”	git cherry-pick -x -m 1 <sha1>
Merge a file from another branch	git checkout solution; git checkout master README.md; git add README.md; commit -m "Merged README from master"
Create and apply a binary patch	git diff-index 79fd4d7 --binary > ~/Desktop/my-patch, Where 79fd4d7 is a placeholder for the commit that came right before the range of commits you want to diff.

So you have a mess on your hands