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#!/usr/bin/env python3
"""PreToolUse hook for Bash: gate `git commit` behind a confirmation modal.
Reads tool-call JSON from stdin. If the Bash command is a `git commit`,
parse the message (HEREDOC or -m forms), list staged files and diff
stats, and emit JSON with permissionDecision=ask and a formatted reason
so the user sees what will actually be committed.
For non-commit Bash calls, exit 0 with no output — default permission
rules apply.
Wire in ~/.claude/settings.json (or per-project .claude/settings.json):
{
"hooks": {
"PreToolUse": [
{
"matcher": "Bash",
"hooks": [
{
"type": "command",
"command": "~/.claude/hooks/git-commit-confirm.py"
}
]
}
]
}
}
"""
import json
import re
import subprocess
import sys
MAX_FILES_SHOWN = 25
MAX_MESSAGE_LINES = 30
def main() -> int:
try:
payload = json.loads(sys.stdin.read())
except (json.JSONDecodeError, ValueError):
return 0 # malformed; don't block
if payload.get("tool_name") != "Bash":
return 0
cmd = payload.get("tool_input", {}).get("command", "")
if not is_git_commit(cmd):
return 0
message = extract_commit_message(cmd)
staged = get_staged_files()
stats = get_diff_stats()
author = get_author()
reason = format_confirmation(message, staged, stats, author)
output = {
"hookSpecificOutput": {
"hookEventName": "PreToolUse",
"permissionDecision": "ask",
"permissionDecisionReason": reason,
}
}
print(json.dumps(output))
return 0
def is_git_commit(cmd: str) -> bool:
"""True if the command invokes `git commit` (possibly with env/cd prefix)."""
# Strip leading assignments and subshells; find a `git commit` word boundary
return bool(re.search(r"(?:^|[\s;&|()])git\s+(?:-[^\s]+\s+)*commit\b", cmd))
def extract_commit_message(cmd: str) -> str:
"""Parse the commit message from either HEREDOC or -m forms."""
# HEREDOC form: -m "$(cat <<'EOF' ... EOF)" or -m "$(cat <<EOF ... EOF)"
heredoc = re.search(
r"<<-?\s*['\"]?(\w+)['\"]?\s*\n(.*?)\n\s*\1\b",
cmd,
re.DOTALL,
)
if heredoc:
return heredoc.group(2).strip()
# One or more -m flags (simple single/double quotes)
flags = re.findall(r"-m\s+([\"'])(.*?)\1", cmd, re.DOTALL)
if flags:
# Multiple -m flags join with blank line (git's own behavior)
return "\n\n".join(msg for _, msg in flags).strip()
# --message=... form
long_form = re.findall(r"--message[=\s]([\"'])(.*?)\1", cmd, re.DOTALL)
if long_form:
return "\n\n".join(msg for _, msg in long_form).strip()
return "(commit message not parseable from command line; will be edited interactively)"
def get_staged_files() -> list[str]:
try:
out = subprocess.run(
["git", "diff", "--cached", "--name-only"],
capture_output=True,
text=True,
timeout=5,
)
return [line for line in out.stdout.splitlines() if line.strip()]
except (subprocess.SubprocessError, OSError, FileNotFoundError):
return []
def get_diff_stats() -> str:
try:
out = subprocess.run(
["git", "diff", "--cached", "--shortstat"],
capture_output=True,
text=True,
timeout=5,
)
return out.stdout.strip() or "(no staged changes — commit may fail)"
except (subprocess.SubprocessError, OSError, FileNotFoundError):
return "(could not read diff stats)"
def get_author() -> str:
"""Report the git author identity that will own the commit."""
try:
name = subprocess.run(
["git", "config", "user.name"],
capture_output=True,
text=True,
timeout=3,
).stdout.strip()
email = subprocess.run(
["git", "config", "user.email"],
capture_output=True,
text=True,
timeout=3,
).stdout.strip()
if name and email:
return f"{name} <{email}>"
return "(git user.name / user.email not configured)"
except (subprocess.SubprocessError, OSError, FileNotFoundError):
return "(could not read git config)"
def format_confirmation(
message: str, files: list[str], stats: str, author: str
) -> str:
lines = ["Create commit?", ""]
lines.append("Author:")
lines.append(f" {author}")
lines.append("")
lines.append("Message:")
msg_lines = message.splitlines() or ["(empty)"]
for line in msg_lines[:MAX_MESSAGE_LINES]:
lines.append(f" {line}")
if len(msg_lines) > MAX_MESSAGE_LINES:
lines.append(f" ... ({len(msg_lines) - MAX_MESSAGE_LINES} more lines)")
lines.append("")
lines.append(f"Staged files ({len(files)}):")
for f in files[:MAX_FILES_SHOWN]:
lines.append(f" - {f}")
if len(files) > MAX_FILES_SHOWN:
lines.append(f" ... and {len(files) - MAX_FILES_SHOWN} more")
lines.append("")
lines.append(f"Stats: {stats}")
lines.append("")
lines.append("Confirm the message, author, and file list before proceeding.")
return "\n".join(lines)
if __name__ == "__main__":
sys.exit(main())
|
