git-commit-msg

#!/bin/bash
# git-commit-msg — generate a commit message from staged (or unstaged) changes using Claude
#
# Inspects the current diff (staged changes first; falls back to all unstaged
# changes if nothing is staged), sends it to Claude to generate a concise
# commit message, then opens your configured git editor pre-filled with the
# generated message so you can review and edit before committing.
#
# Usage:
#   git-commit-msg [-h|--help]
#
# Examples:
#   git-commit-msg          # generate and open editor with commit message
#
# Requirements:
#   claude   Claude CLI (https://claude.ai/code)

_print_help() {
  awk 'NR==1{next} /^#/{sub(/^# ?/,""); print; next} {exit}' "$0"
}

case "$1" in
  -h|--help) _print_help; exit 0 ;;
esac

if ! git rev-parse --git-dir > /dev/null 2>&1; then
  echo "fatal: not a git repository"
  exit 1
fi

if ! command -v claude > /dev/null 2>&1; then
  echo "fatal: claude CLI not found"
  exit 1
fi

diff=$(git diff --cached)
[ -z "$diff" ] && diff=$(git diff)

if [ -z "$diff" ]; then
  echo "fatal: no changes to generate message for"
  exit 1
fi

prompt='Generate a git commit message for this diff.

Rules:
- Output ONLY the commit message — no preamble, no explanation, no markdown
- First line: imperative mood, under 72 characters (e.g. "Fix login timeout", not "Fixed" or "Fixes")
- If the change is non-trivial, add a blank line then a concise body (what changed and why, not how)
- Do not add bullet lists or headers to the body — plain prose only'

echo "Generating commit message..."
message=$(printf '%s' "$diff" | claude -p "$prompt")

if [ -z "$message" ]; then
  echo "fatal: claude returned an empty message"
  exit 1
fi

tmpfile=$(mktemp /tmp/git-commit-msg.XXXXXX)
trap 'rm -f "$tmpfile"' EXIT

printf '%s\n' "$message" > "$tmpfile"
git commit -e -F "$tmpfile"