How to view the change history of a file using Git versioning?

To view the change history of a file in Git, use the commands below to track modifications, authors, and timestamps. Here’s a step-by-step guide with examples:

1. Basic File History

Show all commits affecting a specific file, including diffs (changes):

git log -p <file-path>

Example:

git log -p src/app.js

• -p shows the diff (actual code changes) in each commit.
• Use -- <file> to avoid ambiguity if the filename matches a branch name.

2. Simplified History

List commits in a compact format (author, date, message):

git log --oneline -- <file-path>

Example:

git log --oneline -- README.md

Output:

d3f4a5f Update README
a1b2c3d Add project setup guide

3. Track File Renames

Include commits from before the file was renamed/moved:

git log --follow -p <file-path>

Example:

git log --follow -p docs/new-guide.md  # Tracks history even if renamed from `old-guide.md`

4. View Changes by Author

Filter commits by a specific author:

git log --author="John" -- <file-path>

5. Annotate Line-by-Line Changes

See which commit last modified each line (blame):

git blame <file-path>

Example:

git blame utils/helpers.py

Output:

a1b2c3d (Alice 2023-10-01 14:30:00 -0400 1) def calculate_sum(a, b):
d3f4a5f (Bob   2023-10-02 09:15:00 -0400 2)     return a + b

6. Compare Changes Between Branches

Show commits modifying the file in feature-branch but not in main:

git log main..feature-branch -- <file-path>

7. View Changes Over Time (GUI)

Use Git’s built-in GUI to visualize history:

gitk <file-path>

• GitKraken, VS Code GitLens, or GitHub/GitLab’s web interface also provide visual histories.

Common Scenarios

View changes before a specific date:

git log --until="2023-09-30" -- <file-path>

Find when a bug was introduced:

git log -S "error_message" -- <file-path>  # Search for string in diffs

See only merge commits affecting the file:

git log --merges -- <file-path>

Key Notes

• Replace <file-path> with the file’s relative path (e.g., src/script.js).
• Use git show <commit-hash>:<file-path> to view the file’s content at a specific commit.
• If the file was deleted, use git log -- <file-path> to see its history before deletion.

Example Workflow

1. Check full history with diffs:

   git log -p package.json

2. Find recent changes (last 3 commits):

   git log -3 -p package.json

3. Blame a file to debug a specific line:

   git blame -L 10,20 config.yml  # Lines 10-20

Troubleshooting

• No history found? Ensure the file exists in the repository (check with git ls-files).
• File not tracked? Use git add first to include it in version control.