Git Blame

Git blame is a Git command that annotates each line in a file with the following information.

• The last commit that modified the line.
• The author of the commit.
• The timestamp of the change.
• The line number and code content (optionally).

Syntax

git blame [options] <file-name>

Step-by-Step Guide to use git-blame

To identify the author and commit details for a specific line in a file within a Git repository, use the appropriate Git command as shown below.

Step 1: Move to an empty folder and initialise it with an empty git repository.

Step 2: Clone the required repository from GitHub and navigate to the cloned directory.

Step 3: Run the git blame command with the relative file path to view the author and commit details for each line.

git blame <file-name>

Step 4: To view details for CONTRIBUTING.md in the current directory, run the following command:

git blame CONTRIBUTING.md

Output:

Tip: Observe that the last column of output displays the line number along with the code on that line.

Output study

Let's examine the first line of output:

• Commit ID: Identifies the commit where the line was last modified.
• Author Name: Shows who last changed the line (email can be retrieved if needed).
• Timestamp: Displays when the commit was made (raw format available with -t).

git blame -t CONTRIBUTING.md

Output:

Viewing the commit details

To view detailed information about a specific commit, use the commit ID obtained from the git blame output.

Steps:

1. Copy the commit ID from the git blame result.
   (Example: 46cf3fc43 from CONTRIBUTING.md)
2. Run the following command:

git log -p <commit-id>

Example:

git log -p 46cf3fc43

• git log displays commit history.
• -p / --patch shows author details and code changes (additions and deletions).

Options with git blame

Git provides multiple options to analyze file modifications in detail.

To view output for a range of lines

git blame -L start-line,end-line <file-name>

The below command shows output for lines 2 to 5 both inclusive.

git blame -L 2,5 CONTRIBUTING.md

The output is shown below:

Note: You will get the same output for command - git blame -L 4,+3 README.md. Here 4,+3 signifies output for 3 lines starting from the fourth line.

To view the author email id

git blame -e CONTRIBUTING.md

The above command will show the author's email id instead of the author's name in the result. The output is shown below:

To view changes not older than the given time

git blame --since=3.months CONTRIBUTING.md

• Commits starting with ^ indicate changes made before the specified time.
• In this case, they represent commits older than three months.
• These older commits appear in the git blame output.
• Filter them out to focus only on recent changes.

Output:

git blame --since=3.months CONTRIBUTING.md | grep -v '^\^'

• Use git blame --since=3.months CONTRIBUTING.md to mark commits older than three months.
• Commits prefixed with ^ indicate changes made before the specified time.
• Filter out these older commits to focus on recent changes:

An alternate option to the command line (GUI based)

Git hosting sites like GitHub, Bitbucket, GitLab offer GUI displays for git blame, which gives a clear display of modification history in a file.

Example: GitHub

Step 1: Navigate to the file for which you want to see the modification history and click on the Blame option as shown below.

Step 2: The structure of output is described in the image below :

git blame is a powerful command for analyzing line-level commit history and works effectively with other Git commands for deeper repository inspection.