Introduction to Git

A few things that are useful as I’m learning git.

References

• http://git-scm.com/book

Definitions

• Working Directory - Directory which contains the files of interest. Where you add, remove, and modify the files of interest.
• Index - aka cache. Directory that git uses as a staging area to contain the files and folders ready to be committed to the repository. Git only sees the working directory files after being added to the index. - ref
• Commit - Saves the current index to the repository.
• Repository - Just an overall reference. The .git folder that contains the most recent state of the files you’re working on. You can compress and copy the .git directory to transfer the entire repository.
• Origin - Commonly used branch name for remote repositories.
• Master - Default name for the local repository branch. The “tree trunk” of the branch.
• Branch - A reference to a particular version of your project. Normally everything is done with commits to the master branch. “A branch is basically a commit that’s at the head of an object chain.” - ref. You can delete a branch after merging with the master and not lose any information.
• HEAD - A reference to the current branch that will be committed to.
• Diff between HEAD and index - “Changed things not yet committed.” - ref
• Diff between index and working directory - “Changed things not yet added.” - ref

Commands

• git init - Starts or initializes an empty git repository. Adds the .git directory to your working directory.
• git add - Updates the index using the current content found in the working directory. - ref
  • git add . - Add to index only files created/modified and not those deleted
  • git add -u - Add to index only files deleted/modified and not those created
  • git add -A - Do both operation at once, add to index all files
• git commit - Saves the current content of the index, and information about the changed, added, or removed files, to the repository.
• git commit -a - Combines the git add and git commit command into one line. Be careful as it will add all tracked files to the index and then commit them.
• git status - Lets you know of any changes or differences.
• git remote add <alias> <url> - Adds a remote repository named “alias” to the service at “url”.
• git remote -v - Verifies the remote repository.
• git push <alias> <branch> - Updates the remote repository “alias” with the index from the local repository “branch”.
• git clone <url> - Creates a local git repository from an existing remote repository.
• git merge <diffBranch> - Merges the files changed in the “diffBranch” to the branch you are currently in.
• git log - Shows all commit messages for the current branch.
• git fetch <remoteBranch> - Updates the remote branch information on the local repository.
• git remote remove origin - Remove a remote repository (github, bitbucket, etc.)
• git reset HEAD <file> - Undo a git add <file>.
• git config --list - show git configuration details of repository.

Common Tasks

Write a commit message

1. Be consistent.
2. Separate subject from body with a blank line.
3. Limit subject to 50 characters and body to 72 characters.
4. Capitalize the subject line and don’t end with a period.
5. Use imperative mood in the subject line
   • Fix … (A bug fix)
   • Document … (Documentation only changes)
   • Add … (Add a feature or new code)
   • Remove … (Remove a feature or old code)
   • Change … (Change how a feature works)
   • Refactor … (A code change that neither fixes bugs or adds features)
   • Style … (Changes that do not affect the meaning of the code: white-space, formatting, etc)
   • Tag version … (When pushing new version)
   • Update … (Updating a text post)
6. The body should explain the motivation for the change and contrast this with previous behavior.

Reference Chris Beams and Angular

Create a new remote repository from an existing working directory

1. Set up the .gitignore file to ignore your desired files or folders.

2. Open a terminal in your working directory.

   git init
   git add -A
   git commit -m 'First commit'
   git remote add origin <url>
   git remote -v
   git push origin master
   

Typical work flow

1. Edit files in working directory.
2. git status
3. git add <files>
   • Use git add -p <file> to enter an interactive environment to selectively choose different ‘hunks’ to include or exclude.
     • y adds the current chunk, n skips the current chunk, and s splits the current chunk into smaller pieces so you can select the smaller component.
4. git commit -m "message"
   • or leave off -m to pop up a text editor for the message. the first line is the ‘subject’ and the lines below are for further comments.
5. git push origin master

Reset (delete) the git repository

1. Delete the .git folder of the local project.
2. Create a new git repository.
3. git push --force -u origin master. This will force the remote repository to match the local repository.

Check for differences

• Check for changes between working directory and index of the local repository.

  • git diff
  • git status

• Check for changes between the index and the HEAD (most recent commit of the local repository).

  • git diff –cached
  • git status

• Files that have been added, ready to commit, but not yet committed.

  • git diff HEAD --name-only

• Check for changes between the most recent commit of the local repository and most recent commit of the remote repository.

  git fetch origin/master
  git branch -a
  git diff master origin/master
  

• See the difference between the most recent commit and the previous commit.

  • git diff master^ master

Remove files or folders from the index

• Remove a folder

  • git rm -r --cached <folderName>

• Remove a file

  • git rm --cached <fileName>

Undo a commit.

• git reset --soft HEAD~1
  • Undo previous commit. Useful if commited something unwanted, but have not pushed it yet. Won’t affect files in working tree.

Create .gitignore

• *.ext
  • Won’t track any file with that extension.
• *string
  • Won’t track any file that includes that string.
• dir/
  • Won’t track any directory (in any location) with that name.
• /dir
  • Won’t track any base level directory with that name.
• /dir/**/*.ext
  • Won’t track any .ext file in /dir or any of it’s subdirectories.

Tag a release version

git tag -a v0.1.0 -m 'package version 0.1.0'
git push origin v0.1.0

Split a repository

Suppose your git repository has multiple directories you wish to split into their own git repos. The script from https://github.com/vangorra/git_split will automate this process along with transferring the appropriate git history to the new repository.

Change author name and email

This will leave the commit dates unchanged, but the commit hashes will change.

git filter-branch -f --env-filter "GIT_AUTHOR_NAME='NEW-NAME'; GIT_AUTHOR_EMAIL='NEW-EMAIL'; GIT_COMMITTER_NAME='NEW-NAME'; GIT_COMMITTER_EMAIL='NEW-EMAIL';"
git push origin master --force

Change commit date to author date

The commit hashes will change.

git filter-branch -f --env-filter 'GIT_COMMITTER_DATE=$GIT_AUTHOR_DATE; export GIT_COMMITTER_DATE'
git push origin master --force

Change commit messages

This will change the commit dates and the commit hashes. See my note on reversing commit dates if you do not want them to change. Reference http://stackoverflow.com/a/1186549.

git rebase -i --root # change 'pick' to 'e' to edit
git commit --amend
git rebase --continue

Remove a tracked file or directory after adding to .gitignore

Suppose you previously committed a file or directory and now have added it to the .gitignore. It will still be tracked by git status. If you would like git to forget about this file but are ok with the file staying in the commit history, then run the below.

# for files
git rm --cached <file>
git add .
git commit -m "Removed ignored files"

# for directories
git rm -r --cached <your directory>
git add .
git commit -m "Removed ignored directory"

Solutions for Errors

Increase buffer size

increase the git buffer size if you receive errors trying to upload over https and you have very large files.

# The number of bytes of your largest file in the directory
git config --global http.postBuffer 157286400