Where did this line come from?¶
Consider the What should I commit? chapter. Imagine that we want to know when and why the following text was added:
A helpful guideline is "**commit early, commit often**".
If we can identify the relevant commit, we can then inspect the commit (using git show <commit>) to see all of the changes that it introduced.
Ideally, the commit message will explain the reasons why this commit was made.
This is one way in which your commit messages can act as a lab book.
At the time of writing (commit 2a96324), the contents of the What should I commit? came from two commits:
git log --oneline src/version-control/what-should-I-commit.md
3dfff1f Add notes about committing early and often
9be780b Briefly describe key version control concepts
We can use the git blame command to identify the commit that last modified each line in this file:
git blame -s src/version-control/what-should-I-commit.md
9be780b8 1) # What should I commit?
9be780b8 2)
9be780b8 3) A commit should represent a **unit of work**.
9be780b8 4)
9be780b8 5) If you've made changes that represent multiple units of work (e.g., changing how input data are processed, and adding a new model parameter) these should be saved as separate commits.
9be780b8 6)
9be780b8 7) Try describing out loud the changes you have made, and if you find yourself saying something like "I did X and Y and Z", then the changes should probably divided into multiple commits.
3dfff1fe 8)
3dfff1fe 9) A helpful guideline is "**commit early, commit often**".
3dfff1fe 10)
3dfff1fe 11) ## Commit early
3dfff1fe 12)
3dfff1fe 13) - Don't delay creating a commit because "it's not ready yet".
3dfff1fe 14)
3dfff1fe 15) - A commit doesn't have to be "perfect".
3dfff1fe 16)
3dfff1fe 17) ## Commit often
3dfff1fe 18)
3dfff1fe 19) - Small, focused commits are **extremely helpful** when trying to identify the cause of an unintended change in your code's behaviour or output.
3dfff1fe 20)
3dfff1fe 21) - There is no such thing as too many commits.
You can see that the first seven lines were last modified by commit 9be780b (Briefly describe key version control concepts), while the rest of the file was last modified by commit 3dfff1f (Add notes about committing early and often).
So the text that we're interested in (line 9) was introduced by commit 3dfff1f.
You can inspect this commit by running the following command:
git show 3dfff1f