Automate git bisect

I occasionally use git bisect to figure out where I’ve introduced test failures. If you’re not familiar, given known good and bad commits, along with a test command, git bisect does a binary search over your repo to determine where a bug or test failure was introduced. This is especially useful on large repos with a test suite that takes a minute or two (or more ?) to run.

Most of the time, I just need to check the last handful of commits. To that end, I’ve written a bash function that assumes the current HEAD is bad, 10 commits prior is good, and automatically runs a test command that you define.

gbi() {
	git bisect start
	git bisect bad
	git checkout HEAD~10
	git bisect good
	git bisect run "$@"
}

This won’t cover every case, but should help automate this fairly verbose process most of the time.

Git essentials for SVN users

Coming from Subversion, the extra steps involved in working with a Git repository can be confusing. Here are some basic concepts and commands to get started with Git.

I find that actually doing something is the best way for me to understand. If you’re the same way, the Github tutorial by Code School is great.

Concepts

There are a couple conceptual differences between Git and Subversion that it helps to understand before getting started.

Centralized vs Distributed

Subversion is centralized version control — every commit lives on a central server. Git is distributed version control — everybody has a copy of the repository. When you commit to subversion, the push to the central server is implicit. The commit and push are discrete actions in Git. This means you can do work and commit changes without necessarily being connected to the Git server. Another advantage is the ability to make commits locally without necessarily publishing your work.

File vs Change-based version control

Subversion is file-based — when you make changes and run svn commit, it commits all the changed files by default. Git is changed-based — when you make changes, you have to run git add to “stage” changes. You can get similar behavior to Subversion with git commit -a. The “a” flag tells Git to add all changes in tracked files.

Commands

  • init – Create a new repository.
  • clone – Set up a repository that already exists on a remote server.
  • add – Stage changes to be committed.
  • commit – Add changes to the local repository.
  • push – Push unsynced commits to a remote repository.
  • pull – Pull unsycned commits from a remote repository.

Basic Workflow

  1. Get the latest version of the code. If you already have the repository, you can use git pull to get the latest changes. Otherwise, git clone will download the code from a remote repository and set it up locally. If this is a new repository, you can set it up with git init.

  2. Make changes.

  3. Share your changes. git add <file>; git commit; git push or git commit -a; git push.