Git Command Examples

2021 Mar 2

Checkout a Remote Branch in Local

$ git checkout --track origin/master

The above command creates a local branch with the same name, i.e. master, as the remote branch, and let the local branch track the remote one. “Tracking” means when run git push, Git knows where it pushes changes into.

Some notes from git checkout --help,

As a convenience, –track without -b implies branch creation

-t, –track
When creating a new branch, set up “upstream” configuration.

If no -b option is given, the name of the new branch will be derived from the remote-tracking branch

# assume the Git tag is "0.1.0"
$ git rev-list -n 1 0.1.0 --pretty=format:"%h" | tail -1
c363005

The tag “0.1.0” points to the commit c363005. Use %H if the full SHA1 is needed.

(Search “placeholder” in git show --help for the document of format:<string>.)

Add --abbrev option, like --abbrev=8, if a fixed width SHA1 is needed.

Fix the ^M Character Shown in git diff Result

Sometimes, when run git diff, it prints ^M at the end of some lines. The ^M character represents a carriage-return character, i.e. CRLF, the new line character in Windows. You may see ^M before, if you use Vim to edit some files coming for Windows/DOS. Seeing ^M in the git diff result means the same line was ended with CRLF but now with LF, or vice versa.

Usually, a Git repository should be configured in a way that all text files committed into the repository end with LF, while files checked out end the local machine specific endings, i.e. LF in Unix and CRLF in Windows machines. So that ^M would not be seen in git diff. To fix a repository’s configuration, add a .gitattributes file with content like

# Set the default behavior, in case people don't have core.autocrlf set.
* text=auto

# Declare files that will always have CRLF line endings on checkout.
*.bat text eol=crlf

“Renormalize” all the files with updated configuration.

$ git stash -u
$ git add --renormalize .
$ git status
$ git commit -m "Normalize line endings"
$ git stash pop

See this GitHub doc, Configuring Git to handle line endings, for more details.

git

Avoid Wrong Tracking When Create Branches in Git

2020 Sep 8

Just made a mistake to push commits to a wrong remote branch. Below is the detail.

  1. Need to create a new branch br-x, which needs to be based on the newest remote dev branch.
  2. Run git fetch to get newest change from the remote.
  3. Run git checkout -b br-x origin/dev to create branch br-x.
  4. Change and commit files in branch br-x.
  5. Run git push origin -u br-x to push commits to the remote.

In step 3, the origin/dev is used to as the “start-point” of the new br-x branch. As per git branch --help,

When a local branch is started off a remote-tracking branch, Git sets up the branch (specifically the branch.<name>.remote and branch.<name>.merge configuration entries) so that git pull will appropriately merge from the remote-tracking branch. This behavior may be changed via the global branch.autoSetupMerge configuration flag.

In other words, the git checkout -b br-x origin/dev not only create a new br-x branch, but also let the br-x track the remote dev branch. As a result, in step 5, the git push origin -u br-x doesn’t push commits into a same-name remote branch. However, it pushes commits into the remote dev branch, which the local br-x is tracking since its creation. The remote dev branch is accidentally modified. 😞

To avoid it, one method is use the local dev branch as the “start-point” in step 3. Consider the local dev may be behind the remote dev. You may have to switch to the local dev and git pull to update it first. Another method is using --no-track option, i.e. git checkout -b --no-track br-x origin/dev.

A more thorough method is using git config --global branch.autoSetupMerge false to change the default behavior of Git. When branch.autoSetupMerge is false, when create a branch, Git will not setup its tracking branch even if the “start-point” is a remote-tracking branch. From more details search “branch.autoSetupMerge” in git config --help.

For what is “remote-tracking” branch, check this link. Simply put,

Remote-tracking branch names take the form <remote>/<branch>.

git

Different Emails Addresses for Different Git Repositories

2020 Jun 24

Sometimes, we may want to set up different user emails and user names for different Git repositories. For example, in your personal computer, the user.email is set to your personal email address globally. While committing to your corporate repositories in the personal computer, your corporate email address should be used in the commits. Or you’re working on personal projects on the corporate computer, need to use the personal email for the personal repositories.

Configure Email Address for A Repository

The simplest way is going to each repository, and configuring the user email for each repository specifically.

$ cd /path/to/repo-foo
$ git config user.email email.foo@example.com
$ git config user.name name-foo

The above git config commands write the user.email setting into the .git/config file under the repository.

From git help config, when writing configuration, by default it’s writing to the repository-local configuration file.

When writing, the new value is written to the repository local configuration file by default, and options –system, –global, –worktree, –file can be used to tell the command to write to that location

Examine the Email Address for a Repository

$ cd /path/to/repo-foo
$ git config --list | grep user.email
user.email=email.bar@example.com
user.email=email.foo@example.com

The git config --list above prints more than one user.email values. It’s because, without additional options, the git config --list outputs configuration “merged” from system, global and local.

From git help config,

When reading, the values are read from the system, global and repository local configuration files by default

The git config --list is a read operation. The first user.email value above is from “global”, i.e. ~/.gitconfig. Run git config --list --local | grep user.email to check the repository-local email configuration.

Instead of piping config --list and grep, use git config --get user.email to save some typings.

$ cd /path/to/repo-foo
$ git config --get user.email
user.email=email.foo@example.com

From git help config, --get returns

the last value if multiple key values were found.

Here, the last value is the email from repository-local configuration. The --get can be further omitted, git config user.email has the same result. And git config --get-all user.email is same as git config --list | grep user.email.

Conditional Includes

For new cloned repositories, it’s often to forget to configure the right email addresses for them. The “conditional includes” feature of the git config can save us from this problem.

For example, in your personal computer, all corporate repositories are under ~/corp-repo/. Add a text file called corp-gitconfig there, and edit it as below.

[user]
        name = user-name-for-corp-prj
        email = email-add@your-corp.com

Add below lines in the global git config file, i.e. ~/.gitconfig.

[includeIf "gitdir:~/corp-repo/"]
        path = ~/corp-repo/corp-gitconfig

Now if a new repository is cloned user ~/corp-repo/, the email for that repository is automatically set to email-add@your-corp.com.

git

Git in 2016

2017 Jan 18

这篇文章回顾了Git的一些新功能。

Worktree

通过git worktree,一个Git repository可以有多个工作目录。 如果一段时间内,需要同时工作在一个repository的多个分支上,那么使用worktree比反复切换branch要方便。

$ git worktree add -b hotfix/BB-1234 ../hotfix/BB-1234

Bisect

git bisect不是一个特别新的功能。用它方便地定位出问题的commit(假设test case充足的话)。

$ git bisect start
$ git bisect good v2.0.0
$ git bisect bad master
$ git bisect run npm test

Autostash

$ git config --global rebase.autostash true

这样就不怕每次rebase前忘记git stash了。

Simple Stash IDs

不需要输入git stash apply stash@{n},简单地输入git stash apply 1就可以了。

更多的内容,请阅读原文。

git