The Power of the Log

As a project grows, the history becomes a massive database of changes. git log is the query language for this database. Using it effectively can save you hours of debugging.

Formatting the Log

The default git log is verbose. To get a high-level overview, you can customize the output format.

One-line

git log --oneline

This shows just the abbreviated SHA and the commit message.

Decorating

To see where branches and tags are pointing:

git log --oneline --decorate

Graphing

To visualize the branching history in the terminal:

git log --oneline --graph --all

This draws an ASCII art tree of your commit history, showing merges and divergences.

Filtering History

You often want to find specific commits rather than listing everything.

By Time

git log --since="2 weeks ago"
git log --until="2023-01-01"

By Author

git log --author="Linus"

By File

To see only commits that modified a specific file:

git log -- path/to/file.py

By Content (Search)

To search for commits that added or removed a specific string (the “Pickaxe”):

git log -S "functionName"

Inspecting Commits

If git log lists the commits, git show inspects the details of a single object.

git show a1b2c3d

This displays the log message and the diff of what changed in that commit.

Blaming

When you encounter a bug, you often want to know: “Who wrote this line and when?” git blame annotates each line of a file with the commit information.

git blame main.c

Output:

^4a2b3c (Alice 2023-01-01 10:00:00 +0000 1) int main() {
8d7e6f (Bob   2023-01-02 11:00:00 +0000 2)     return 0;
^4a2b3c (Alice 2023-01-01 10:00:00 +0000 3) }

In many IDEs, this functionality is integrated as “Git Lens” or “Annotate”.

Reflog: The Safety Net

Git keeps a log of where your HEAD pointer has been, even if you deleted branches or reset commits. This is called the “Reference Log” or reflog.

git reflog

It shows a local history of your actions (switching branches, resetting, committing). It is invaluable for recovering “lost” commits.

# Initialize and create some history
git init
echo "one" > file.txt
git add file.txt
git commit -m "First commit"
echo "two" >> file.txt
git commit -am "Second commit"
echo "three" >> file.txt
git commit -am "Third commit"

# Show only the last 2 commits
git log -n 2 --oneline

... Third commit
... Second commit

Diffing

We’ve used git diff to see working directory changes. But it is much more powerful.

Comparing Branches

To see what is in feature that is not in main:

git diff main..feature

Comparing Commits

To see the difference between two specific points in time:

git diff HEAD~2 HEAD

# Complete the command to show a decorated, one-line graph of all branches
git log --oneline --decorate --graph --all

# Complete the command to show a decorated, one-line graph of all branches
git log --oneline --decorate --graph --