Q: You need to find out who last changed a specific line in a file, when they changed it, and why. Walk me through how you'd investigate.

Start with git blame:

• git blame --ignore-rev skips a known bulk-formatting commit. Create a .git-blame-ignore-revs file listing such commits and configure it globally.
• git blame -w ignores whitespace changes.
• git blame -C detects code moved or copied from other files.

This shows the commit SHA, author, date, and content for line 42. The -L flag limits output to specific lines (-L 40,50 for a range). To understand *why* the change was made: If the blame shows a commit like "Apply formatting" (not the real author), dig deeper: This blames the file at the commit *before* the formatting change. Or use git log -L 42,42:src/auth/login.js to see the full history of changes to that specific line range — every commit that touched those lines, with diffs. For files that have been renamed, add --follow: Pro tips:

git blame -L 42,42 src/auth/login.js