Debugging with git

The setup script is located in the git.zip file in the exercsises folder.

Run ./debugging.sh for setup! Then change into the directory with cd debugging.

git blame

git blame annotates each line with commit it was last changed. It can also detect movements and copies of lines.

Instructions

1. Run git blame -C file2.txt
2. Run git show to show the last commit
3. Run git blame file2.txt

HINT: In the past there were issues with certain git versions on MacOS.

Questions

• What lines are moved from where?
• What is the default lower limit for git to consider a line copied or moved?
• Who edited the moved lines?
• According to the commit, who is the author?
• According to the standard blame, who is the author?

Answers

• the second line is moved
• 20 chars
• Your configured user, in my case maschmi
• Hans
• Hans

git bisect

Imagine the following situation. Sometime during the last weeks a subtle bug was introduced. You have no idea when and where this happened. Lucky for you, the team does rather small commits and now it is only a question to find the specific commit. Even better, there is a simple, automatic test to detect the bug. git bisect helps you to find this commit fast!

Preparations

1. Run ./test.sh and watch the test fail
2. We assume the commit with add new stuff to file1 was a good commit. Run git log --oneline to find the commit hash
3. Run git checkout commitHash to check this out this revision (we detach the head and check out this revision)
4. Run ./test.sh again and watch if succeed
5. Run git checkout debugging to switch to back to the debugging branches HEAD

Bisecting

HINT: There are two aliases defined

• git good => git bisect good
• git bad => `git bisect bad

1. Run git bisect start
2. Mark the current HEAD as bad with git bisect bad
3. Mark the commitHash from the good commit as good with git bisect good commitHash
4. Now we start the loop: Run ./test.sh and then either git bisect bad or git bisect good
5. Stop when a commit is printed
6. Run git bisect reset to exit bisect mode

Questions

• How many steps were needed to find the commit?
• Which commit introduced the failure?

Answers

• 7
• commit 33