drn/amend

Amend Last Commit

Rewrite the last commit message with a clear, descriptive summary based on the actual changes.

Arguments

• $ARGUMENTS - Optional: specific instructions for the commit message (e.g., "mention the performance improvement")

Context

• Current branch: !git branch --show-current
• Last commit: !git log -1 --format="%H %s" 2>/dev/null | head -1
• Last commit body: !git log -1 --format="%b" 2>/dev/null | head -20
• Diff stat: !git diff HEAD~1 --stat 2>/dev/null | head -30

Instructions

Step 1: Understand the changes

1. Read the diff of the last commit: git diff HEAD~1 (full diff, not just stat)
2. Read any files that were added or significantly changed to understand their purpose
3. Check the current commit message — if it's already descriptive and accurate, tell the user and stop

Step 2: Draft the message

Write a commit message following this structure:

Subject line (first line):

• Imperative mood ("Add", "Fix", "Update", not "Added", "Fixes")
• Under 72 characters
• Summarize WHAT changed and WHY at a high level
• No trailing period

Body (separated by blank line, optional but preferred for non-trivial changes):

• Explain what the change does and why it was made
• Wrap lines at 72 characters
• Focus on context that isn't obvious from the diff
• Skip the body for truly trivial changes (typo fixes, version bumps)

Step 3: Amend the commit

Run git commit --amend with the new message. Use a HEREDOC to pass the message:

git commit --amend -m "$(cat <<'EOF'
Subject line here

Body paragraph here explaining the change in more detail.
EOF
)"

Step 4: Confirm

Show the user the new commit with git log -1 so they can verify.

Rules

• Never change the commit contents — only the message. Do not stage or unstage files.
• Preserve co-author trailers from the original message if present.
• If the working tree has staged changes, warn the user that --amend will include them, and ask before proceeding.
• If $ARGUMENTS contains specific instructions, incorporate them into the message.