Manual - Git

Everything about using Git from the command line - from practical tips and tricks to clever bash snippets.

Only clone a single branch

git clone <url> --branch <branch> --single-branch <folder>

Change the author of the last commit in git

git commit --amend --author "New Author Name <correct-email-address@domain.com>"

Update user email address in all commits

git filter-branch -f --env-filter '
OLD_EMAIL="liwenkz@asos.com"
CORRECT_NAME="Liwen Knight-Zhang"
CORRECT_EMAIL="development@liwen.name"
if [ "$GIT_COMMITTER_EMAIL" = "$OLD_EMAIL" ]
then
    export GIT_COMMITTER_NAME="$CORRECT_NAME"
    export GIT_COMMITTER_EMAIL="$CORRECT_EMAIL"
fi
if [ "$GIT_AUTHOR_EMAIL" = "$OLD_EMAIL" ]
then
    export GIT_AUTHOR_NAME="$CORRECT_NAME"
    export GIT_AUTHOR_EMAIL="$CORRECT_EMAIL"
fi
' --tag-name-filter cat -- --branches --tags

then

git push --force --tags origin 'refs/heads/#'

Using git-log to get repo stats

# number of releases (git tags based) in a given date range
git log --tags --since=2020-07-01 --until=2021-06-30 --simplify-by-decoration --pretty="format:%ai %d" | grep "tag: v" | wc -l
 
# line of code changed
git log --since=2020-07-01 --until=2021-06-30 --format= --numstat | awk '{s+=$1; s+=$2} END {print s}'

Copy all branches to a different repository

for remote in `git branch -r | grep -v master `; do git checkout --track $remote ; done
git push --all

Git worktree

Git worktree lets you check out multiple branches from the same repository into separate directories. Each worktree has its own working directory with isolated files, while sharing the same Git history.

Create a new worktree:

# Create a new worktree with a new branch 
# Assume .worktrees is the directory you keep the worktrees
git worktree add .worktrees/feature-a -b feature-a
 
# Or create a worktree with an existing branch
git worktree add .worktrees/bugfix-slugs bugfix-123

Manage worktrees:

# List all worktrees
git worktree list
 
# Remove a worktree when done
git worktree remove ../project-feature-a
 
# Don't forget to delete the branch after removing the worktree
git branch -D feature-a

diff against a tag to see accumulated changes

git diff scope-statement-v1.1 -- policies-processes-governance/scope-statement.md 
 
git diff statement-of-applicability-v1.1 -- policies-processes-governance/statement-of-applicability.md

Working with GitHub

Using multiple GitHub accounts with SSH keys

To use two separate GitHub accounts with two different SSH keys on the same computer, you can define host aliases in ./ssh/config to distinguish them.

Host github-lwkz
 HostName github.com
 User lwkz
 AddKeysToAgent yes
 UseKeychain yes
 IdentityFile ~/.ssh/id_rsa
 
Host github-spd
 HostName github.com
 User lwkz-spd
 AddKeysToAgent yes
 UseKeychain yes
 IdentityFile ~/.ssh/id_rsa_SPD

Add SSH private keys to your SSH agent as usual:

ssh-add ~/.ssh/id_rsa
ssh-add ~/.ssh/id_rsa_SPD

Test connections:

ssh -T git@github.com
ssh -T git@github-spd

You should see something like this:

Hi lwkz! You've successfully authenticated, but GitHub does not provide shell access.
Hi lwkz-spd! You've successfully authenticated, but GitHub does not provide shell access.

Clone your repositories using aliases defined earlier:

git clone git@github.com:lwkz/repo.git
git clone git@github-spd:news-lwkz/repo.git # Notice the @github-spd host