`git`¶

Worktrees¶

git worktree allows to have multiple working directories for a single repository. A worktree is the same as a normal repository, with the caviet that it is not possible to checkeout the same branch in multiple worktrees.

This is useful for working on multiple features in parallel, and avoids the need to stash changes or create multiple clones of the repository.

Create a new worktree¶

git worktree add -b <BRANCH> <PATH>

Convention

Clone the repository as <REPO>.<DEFAULT_BRANCH> and create worktrees for features as <REPO>.<FEATURE_BRANCH>. This is my own convention and it is not a standard.

Aliases¶

git allows to create aliases for common commands.

Aliases can be created in the global configuration as follows:

git config --global alias.<ALIAS> <COMMAND>

My configuration

[alias]
    aa = add --all
    co = checkout
    cob = checkout -b
    cs = commit -signed --signoff
    discard = reset HEAD --hard
    fp = push --force-with-lease
    lol = log --graph --decorate --pretty=oneline --abbrev-commit
    lola = log --graph --decorate --pretty=oneline --abbrev-commit --all
    pr = "!f() { git fetch --force origin pull/$1/head:pr-$1; }; f"
    ps = push --signed
    root = rev-parse --show-toplevel
    st = status
    stag = tag -l --sort=v:refname
    uncommit = reset --soft HEAD^
    unstage = reset HEAD --
    wt = worktree

--force-with-lease

--force-with-lease is a safer alternative to --force that does not overwrite changes on the remote branch.

Identity¶

Signing commits¶

git supports signing commits with GPG keys.

Create GPG keys

gpg --default-new-key-algo rsa4096 --gen-key
gpg --armor --export <KEY_ID> # (1)!

Export public key. This can be used to add the key to GitHub, etc.

List available GPG keys

gpg --list-secret-keys --keyid-format=long

git config --global --unset gpg.format # (1)!
git config --global user.signingkey 3AA5C34371567BD2

One could use different key formats, such as SSH keys. Here we want to use GPG keys.

Signing keys can also be added to specific configurations or repositories. See Conditional configuration for separate work and personal configurations.

Signoff commits¶

git commit supports the --signoff option to add a signoff line to the commit message.

This is useful to indicate that the author has the right to submit the code.

git commit --signoff

Bisection¶

git bisect allows to find the commit that introduced a bug by performing a binary search.

To starti bisecting, use:

git bisect start

Then mark the current commit as bad:

git bisect bad

and mark a known good commit:

git bisect good <COMMIT>

git bisect will then checkout a commit in the middle of the range and ask to mark it as good or bad. This process is repeated until the commit that introduced the bug is found.

Correct a bisection mistake¶

If a commit is marked as good or bad by mistake, it can be corrected with the following steps:

Save the current bisection log to a file
```
git bisect log > bisect.log
```
Reset the bisection state
```
git bisect reset
```
Amend the bisection log file to remove the incorrect entry
Restart the bisection with the corrected log
```
git bisect replay bisect.log
```

git bisect log

git bisect start
# status: waiting for both good and bad commits
# good: [0128dc24c6d018b61ceaac080640014e1d5ec344] Update README
git bisect good 0128dc24c6d018b61ceaac080640014e1d5ec344
# bad: [25935e1a7e022ede9fd71bd86dcbaa7a3f1846b7] Merge pull request #85 from gdonval/fix-malloc
git bisect bad 25935e1a7e022ede9fd71bd86dcbaa7a3f1846b7
# bad: [637a6e5f2953263d4f05574c8d6037356a81b9ea] Merge pull request #65 from Reference-ScaLAPACK/weslleyspereira-fix-cmake-requirements
git bisect bad 637a6e5f2953263d4f05574c8d6037356a81b9ea
# good: [681a6cf436360a3f5121f224a026150795283e56] Merge pull request #56 from weslleyspereira/try-CI
git bisect good 681a6cf436360a3f5121f224a026150795283e56

Tip

One could add the following git alias to undo the last action automatically:

alias bisect-undo='git bisect log | head -n -2 > /tmp/git-fixed-bisect.txt && git bisect reset && git bisect replay /tmp/git-fixed-bisect.txt && rm /tmp/git-fixed-bisect.txt'

Cherrypicking changes¶

git add allows to interactively select hunks to stage form different files:

git add -p

This allows to create atomic commits by interactively selecting changes to be staged.

Large Repositories¶

When cloning large repositories, setting feature.manyFiles enables configuration options to improve performance:

git clone -c feature.manyFiles=true <REPO>

Diff for staged files¶

git diff does not show staged files in the diff.

The --staged option can be used to show the diff for staged files:

git diff --staged

Global ignore file¶

A global git ignore file can be created to ignore files across all repositories. This is useful for files that are specific to a certain workflow (.envrc, ...) or editor (.vscode, .idea), but not relevant to the repository.

The global ignore file can be created by setting the core.excludesfile configuration:

git config --global core.excludesfile ~/.config/git/ignore

Typically, the file is stored under ~/.config/git/ignore. To check if the global ignore file already exists, use:

git config --get core.excludesfile

Excluded files

.envrc
.vscode/
.idea/
core*
.null-ls_*

Conditional configuration¶

git supports conditional configurations to include configurations based on conditions. A common use-case is to have different configurations for work and personal repositories.

Separate work and personal configurations

If work repositories are under ~/git/work and personal repositories are under ~/git/oss, the following configuration can be used:

[includeIf "gitdir:~/git/work/"]
    path = ~/git/work/.config
[includeIf "gitdir:~/git/oss/"]
    path = ~/git/oss/.config

~/git/work/.config~/git/oss/.config

[user]
    name = John Doe
    email = john.doe@work.com

[user]
    name = John Doe
    email = john.doe@oss.org

Clean up¶

Some workflows produce a lot of temporary files that are not tracked by git. It is sometimes useful to clean up these files to have the repository in a clean state. To clean up untracked files, use:

git clean -fd

The command above will remove all untracked files and directories.

Danger

Be careful with git clean -fd as it will remove all untracked files and directories. It is recommended to perform a dry run with

git clean -nfd

to see what files will be removed.

Revert changes from a specific file¶

The git revert command can be used to revert a specific commit. However, this reverts all the files changed in that commit. To revert changes from a specific file, use the git checkout command:

git checkout <COMMIT>~ -- <FILE>

~

<rev>~[<n>] refers to the <n>-th generation ancestor of <rev>.

To revert the changes introduced by a specific commit <COMMIT>, we checkout the file from the commit before it (<COMMIT>~).

git¶