lib-cli-exit-tools 2.3.0
CLI exit handling helpers: clean signals, exit codes, and error printing
License: MIT
Requires Python: >=3.10
Keywords: cli, click, errors, exit, signals

# lib_cli_exit_tools

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Small helpers for robust CLI exit handling:
- Portable signal handling (SIGINT, SIGTERM/SIGBREAK)
- Consistent exception → exit code mapping
- Concise error printing with optional traceback and subprocess stdout/stderr capture

## Why lib_cli_exit_tools?

Building CLI applications that behave correctly in shell pipelines, CI/CD systems, and across platforms is surprisingly tricky. This library solves five common pain points:

1. **Correct Exit Codes** — Exceptions are automatically mapped to platform-appropriate exit codes (POSIX errno or BSD sysexits). `FileNotFoundError` returns `2`, `PermissionError` returns `13` on POSIX, and `KeyboardInterrupt` returns `130` — matching shell conventions without manual bookkeeping.

2. **Portable Signal Handling** — SIGINT (Ctrl+C), SIGTERM, and Windows SIGBREAK are translated into structured Python exceptions with deterministic exit codes. Your CLI behaves consistently whether terminated by a user, a process manager, or a CI runner.

3. **Clean Error Output** — Uncaught exceptions produce concise, coloured error messages by default. Toggle `--traceback` for full Rich-formatted stack traces during debugging — no code changes required.

4. **Pipeline-Friendly** — `BrokenPipeError` is handled gracefully (exit 141 by default, matching `128 + SIGPIPE`), so piping output to `head` or other truncating tools doesn't produce noisy tracebacks.

5. **Zero Boilerplate** — Wrap any Click command with `run_cli()` and get signal handling, exit-code translation, and stream flushing in one call. Configuration is centralised and test-friendly via context managers.

## Install

Requires Python 3.10 or newer.

```bash
pip install lib_cli_exit_tools
```

See [INSTALL.md](INSTALL.md) for editable installs, pipx/uv usage, and troubleshooting tips.

## Usage

Console script (all commands map to ``lib_cli_exit_tools.cli:main``):

```bash
# After install (pip/pipx/uv tool)
lib-cli-exit-tools --help
lib-cli-exit-tools info
lib-cli-exit-tools fail  # intentionally trigger RuntimeError to test error paths
# Aliases are also generated: `cli-exit-tools`, `lib_cli_exit_tools`
```

## CLI Reference

The library installs three equivalent console scripts: `lib-cli-exit-tools` (primary), `cli-exit-tools`, and `lib_cli_exit_tools`. All invoke `lib_cli_exit_tools.cli:main`.

### Global Options

| Option | Default | Description |
|--------|---------|-------------|
| `--traceback` / `--no-traceback` | `False` | Show full Python traceback on errors |
| `--version` | — | Show program version and exit |
| `-h`, `--help` | — | Show help message and exit |

### Commands

#### `info`
Display package metadata (name, version, homepage, author).

```bash
lib-cli-exit-tools info
```

#### `fail`
Intentionally raise `RuntimeError('i should fail')` to validate error handling paths.

```bash
lib-cli-exit-tools fail
lib-cli-exit-tools --traceback fail  # show full traceback
```

### Examples

The snippets below move from a minimal “hello world” through a production-ready
CLI that demonstrates configuration hooks and structured error handling.

#### 1. Minimal command (copy-paste ready)

```python
from __future__ import annotations

import rich_click as click

from lib_cli_exit_tools import run_cli


@click.command()
def hello() -> None:
    """Say hello with automatic signal-aware exit handling."""
    click.echo("Hello from lib_cli_exit_tools!")


if __name__ == "__main__":
    raise SystemExit(run_cli(hello))
```

Run it with:

```bash
python hello.py
```

#### 2. Traceback-mode helper using `cli_session`

```python
from __future__ import annotations

import rich_click as click

from lib_cli_exit_tools import cli_session


@click.command()
def failable() -> None:
    """Command that always fails to demonstrate traceback handling."""
    raise RuntimeError("toggle --traceback to see the full traceback")


def main(*, traceback: bool = False) -> int:
    """Run failable with optional traceback display."""
    with cli_session(overrides={"traceback": traceback}) as run:
        return run(failable)


if __name__ == "__main__":
    import sys

    enable_traceback = "--traceback" in sys.argv
    raise SystemExit(main(traceback=enable_traceback))
```

Running `python cli.py --traceback` enables coloured tracebacks for that
session. The `cli_session` context manager restores configuration afterwards.

#### 3. Full-featured multi-command CLI

```python
from __future__ import annotations

import json
import sys
from dataclasses import dataclass

import rich_click as click

from lib_cli_exit_tools import SignalSpec, cli_session, default_signal_specs


@dataclass(slots=True)
class Settings:
    pretty: bool


@click.group()
@click.option("--pretty/--no-pretty", default=True)
@click.pass_context
def cli(ctx: click.Context, pretty: bool) -> None:
    ctx.obj = Settings(pretty=pretty)


@cli.command()
@click.pass_obj
def info(settings: Settings) -> None:
    payload = {"pretty": settings.pretty}
    click.echo(json.dumps(payload, indent=2 if settings.pretty else None))


@cli.command()
@click.pass_obj
def fail(settings: Settings) -> None:
    click.echo("About to fail…")
    raise RuntimeError("intentional failure for diagnostics")


def main() -> int:
    # Parse --traceback early before entering cli_session
    traceback = "--traceback" in sys.argv
    argv = [arg for arg in sys.argv[1:] if arg != "--traceback"]

    overrides = {"traceback": traceback, "traceback_force_color": traceback}
    signals: list[SignalSpec] = default_signal_specs()
    with cli_session(overrides=overrides) as execute:
        return execute(cli, argv=argv, signal_specs=signals)


if __name__ == "__main__":
    raise SystemExit(main())
```

This version parses `--traceback` early (before Click sees it), then wires
configuration overrides, custom signal specs, and multiple commands into a
single composition point—mirroring how a production CLI can layer policy logic
around Click while still delegating exit-code translation to `lib_cli_exit_tools`.

#### 4. Custom signal handlers

`run_cli` accepts an explicit `signal_spec` sequence and a `signal_installer`
hook so you can provide bespoke behaviour. The example below installs a custom
SIGUSR1 handler alongside the library defaults:

```python
from __future__ import annotations

import signal
from contextlib import ExitStack
from typing import Callable

import rich_click as click

from lib_cli_exit_tools import SignalSpec, default_signal_specs, run_cli


CUSTOM_SIG = getattr(signal, "SIGUSR1", None)


def custom_signal_specs() -> list[SignalSpec]:
    specs = default_signal_specs()
    if CUSTOM_SIG is not None:
        specs.append(
            SignalSpec(
                signum=CUSTOM_SIG,
                exception=RuntimeError,
                message="Received SIGUSR1",
                exit_code=75,
            )
        )
    return specs


def install_custom_signals(specs: list[SignalSpec] | None) -> Callable[[], None]:
    stack = ExitStack()

    for spec in specs or []:
        def _handler(signum: int, frame: object | None, *, spec: SignalSpec = spec) -> None:
            raise spec.exception(f"Signal {spec.message}")

        try:
            previous = signal.getsignal(spec.signum)
            signal.signal(spec.signum, _handler)
        except OSError:
            continue
        stack.callback(signal.signal, spec.signum, previous)

    return stack.close


@click.command()
def main() -> None:
    click.echo("Send SIGUSR1 to trigger the custom handler...")
    if hasattr(signal, "pause"):
        signal.pause()


if __name__ == "__main__":
    custom_specs = custom_signal_specs()
    raise SystemExit(
        run_cli(
            main,
            signal_specs=custom_specs,
            signal_installer=install_custom_signals,
        )
    )
```

The `signal_installer` callable receives the resolved `SignalSpec` list and
must return a zero-argument restorer. In this case, the helper installs handlers
via `ExitStack`, raising the specified exception whenever the signal fires and
restoring the previous handlers once `run_cli` completes.

Library:

```python
import lib_cli_exit_tools

lib_cli_exit_tools.config.traceback = False  # show short messages
try:
    raise FileNotFoundError("missing.txt")
except Exception as e:
    code = lib_cli_exit_tools.get_system_exit_code(e)   # 2 on POSIX
    lib_cli_exit_tools.print_exception_message()        # prints: FileNotFoundError: missing.txt
    raise SystemExit(code)
```

Command names registered on install (all invoke ``lib_cli_exit_tools.cli:main``)
- lib-cli-exit-tools (default console script)
- cli-exit-tools (alias)
- lib_cli_exit_tools (alias)
- python -m lib_cli_exit_tools (module entry)

If you installed with --user or in a venv, make sure the corresponding bin directory is on PATH:
- Linux/macOS venv: .venv/bin
- Linux/macOS user: ~/.local/bin
- Windows venv: .venv\Scripts
- Windows user: %APPDATA%\Python\PythonXY\Scripts

### Runtime configuration

All configuration lives on the module-level `lib_cli_exit_tools.config` object. Adjust it once during startup; the settings apply process-wide:

```python
from lib_cli_exit_tools import config

config.traceback = True              # emit full tracebacks instead of short messages
config.exit_code_style = "sysexits"  # emit BSD-style exit codes (EX_USAGE, EX_NOINPUT, …)
config.broken_pipe_exit_code = 0     # treat BrokenPipeError as a benign truncation
```

Field reference:

| Field | Type | Default | Description |
|-------|------|---------|-------------|
| `traceback` | `bool` | `False` | When `True`, `handle_cli_exception` renders a full Rich traceback to stderr. The bundled CLI toggles this via `--traceback/--no-traceback`. |
| `exit_code_style` | `"errno"` \| `"sysexits"` | `"errno"` | Controls exit code mapping. `errno` returns POSIX/Windows-style codes; `sysexits` returns BSD-style semantic codes (EX_USAGE, EX_NOINPUT, etc.). |
| `broken_pipe_exit_code` | `int` | `141` | Exit status for `BrokenPipeError` (default mirrors `128 + SIGPIPE`). Set to `0` to treat truncation as success. |
| `traceback_force_color` | `bool` | `False` | Force Rich to emit ANSI-coloured tracebacks even when stderr is not a TTY. Useful for CI logs. |

Remember that `config` is module-level—if you call the library from multiple threads or embed it in another CLI, configure it once during bootstrap before handing control to user code. When you need temporary overrides (for tests or nested CLIs), wrap the change with the built-in context manager so state is restored automatically:

```python
from lib_cli_exit_tools import config_overrides, config

with config_overrides(traceback=True):
    # tracebacks enabled only within this block
    run_something()

# state restored to previous values here
```

To return to baseline defaults, call `lib_cli_exit_tools.reset_config()`.

## Testing

Install the project with development extras before running the full test matrix:

```bash
pip install -e .[dev]
```

Afterwards, execute the consolidated quality gate:

```bash
make test
```

Need to run coverage manually without the helper? Use the new convenience target so
you never depend on a platform-specific `coverage` shim:

```bash
make coverage
```

Which internally delegates to the scripts toolbox:

```bash
python -m scripts coverage
```

The target expands to `python -m coverage run -m pytest -vv` and therefore works
even when the `coverage` console script is not available on your PATH. The helper
also sets `COVERAGE_NO_SQL=1` ahead of each run so coverage falls back to the
file-based data format instead of SQLite, avoiding "database is locked" errors
on shared workstations.

Prefer the automation CLI when you need to tweak options without editing the
Makefile:

```bash
python -m scripts.test --coverage=off --verbose
```

The suite includes OS-aware cases (POSIX, Windows-specific signal handling), so
run it on each target platform you support to keep coverage consistent.

If your environment reports “cannot execute” when running `pytest`, the auto-generated entry-point script likely points at a removed interpreter. Reinstall the dev extras or invoke tests with `python -m pytest` (for example, `python -m pytest tests/`).

When coverage uploads are skipped (no Codecov token), `make test` still writes `coverage.xml` and `codecov.xml` to the project root so you can inspect results locally or feed them into other tooling.

## Public API Reference

The package re-exports the helpers below via `lib_cli_exit_tools.__all__`. Import them directly with `from lib_cli_exit_tools import …`.

### `config`
Mutable dataclass-like singleton holding process-wide settings. Configure it during CLI startup.

- `traceback` (`bool`): `True` to surface full Python tracebacks; `False` keeps short, coloured summaries.
- `exit_code_style` (`'errno' | 'sysexits'`): Selects POSIX/Windows errno-style exit codes or BSD `sysexits` semantics.
- `broken_pipe_exit_code` (`int`): Overrides the exit status for `BrokenPipeError` (default `141`).
- `traceback_force_color` (`bool`): Forces Rich-coloured tracebacks even when stderr is not a TTY.

### `run_cli(cli, argv=None, *, prog_name=None, signal_specs=None, install_signals=True, exception_handler=None, signal_installer=None) -> int`
Wrap a Click command or group so every invocation shares the same signal handling and exit-code policy. Returns the numeric exit code instead of exiting the process.

Parameters:
- `cli`: `click.BaseCommand` to execute.
- `argv`: Iterable of CLI arguments (excluding the program name) or `None` to defer to Click's defaults.
- `prog_name`: Override the program name shown in help/version output.
- `signal_specs`: Iterable of `SignalSpec` objects to customise signal handling; defaults to `default_signal_specs()`.
- `install_signals`: Set `False` when the host application already manages signal handlers.
- `exception_handler`: Callable receiving the raised exception and returning an exit code; defaults to ``handle_cli_exception``.
- `signal_installer`: Callable mirroring ``install_signal_handlers`` for embedding scenarios.

### `cli_session(*, summary_limit=500, verbose_limit=10_000, overrides=None, restore=True)`
Context manager that snapshots `lib_cli_exit_tools.config`, optionally
applies temporary overrides, and yields a callable compatible with
`run_cli`.

Parameters:
- `summary_limit` (`int`, default `500`): Character budget when tracebacks are disabled.
- `verbose_limit` (`int`, default `10_000`): Character budget when tracebacks are enabled.
- `overrides` (`Mapping[str, object] | None`, default `None`): Mapping of configuration field/value pairs applied during the session. When `traceback` is supplied and `traceback_force_color` is omitted, colour output is automatically forced.
- `restore` (`bool`, default `True`): When `True`, configuration state is restored after the session. Set to `False` to leave overrides in place once the context exits.

Use it to restore configuration automatically—even when the wrapped command
raises:

```python
from lib_cli_exit_tools import cli_session

with cli_session(overrides={"traceback": True}) as run:
    exit_code = run(my_click_command, argv=["--help"])
```

### `handle_cli_exception(exc, *, signal_specs=None, echo=None) -> int`
Translate exceptions raised by Click commands into deterministic exit codes, honouring configured signal mappings and traceback policy.

Parameters:
- `exc`: Exception instance to classify.
- `signal_specs`: Optional iterable of `SignalSpec` objects for custom signal handling.
- `echo`: Callable matching `click.echo` signature, allowing custom stderr routing during tests or embedding.

### `get_system_exit_code(exc) -> int`
Compute a platform-aware exit status for arbitrary exceptions (errno mappings on POSIX/Windows or BSD `sysexits` when enabled).

Parameters:
- `exc`: Exception instance to classify.

### `print_exception_message(trace_back=None, length_limit=500, stream=None) -> None`
Emit the active exception using Rich formatting. Produces a coloured traceback when `trace_back` is `True`, otherwise prints a truncated summary in red. Respects `config.traceback_force_color` and mirrors the behaviour of `handle_cli_exception` (tracebacks are rendered before the helper returns an exit status).

Parameters:
- `trace_back`: Toggle between full traceback rendering (`True`) and short summary (`False`). When `None` (default), uses `config.traceback`.
- `length_limit`: Maximum characters for summary output.
- `stream`: Target text stream; defaults to `sys.stderr`.

### `i_should_fail()`
Deterministically raise `RuntimeError('i should fail')` to exercise error-handling paths. Useful for smoke-testing exit-code translation, CLI traceback toggles, and log formatting without inventing ad-hoc failing commands.

### `flush_streams() -> None`
Best-effort flush of `sys.stdout` and `sys.stderr`, ensuring buffered output is written before exit.

### `default_signal_specs() -> list[SignalSpec]`
Return the default signal mapping for the current platform (always includes `SIGINT`, plus `SIGTERM`/`SIGBREAK` when available).

### `install_signal_handlers(specs=None) -> Callable[[], None]`
Register handlers that raise structured exceptions for the provided specs and return a restoration callback. Invoke the callback (typically in a `finally` block) to restore previous handlers.

Parameters:
- `specs`: Iterable of `SignalSpec` objects; defaults to `default_signal_specs()`.

### `SignalSpec(signum: int, exception: type[BaseException], message: str, exit_code: int)`
Lightweight dataclass describing how a signal maps to an exception, stderr message, and exit code.

Fields:
- `signum`: Numeric signal value passed to `signal.signal`.
- `exception`: Exception type raised by the handler.
- `message`: Human-readable text echoed when the signal fires.
- `exit_code`: Exit status returned to the OS.

### `CliSignalError` and subclasses
Hierarchy of marker exceptions raised when signal handlers trigger. Use them to differentiate signal-driven exits from other failures.

- `CliSignalError`: Base class.
- `SigIntInterrupt`: Raised on `SIGINT` (Ctrl+C); maps to exit code `130`.
- `SigTermInterrupt`: Raised on `SIGTERM`; maps to exit code `143`.
- `SigBreakInterrupt`: Raised on Windows `SIGBREAK`; maps to exit code `149`.

### `default_signal_specs`, `install_signal_handlers`, and `run_cli` contract summary
When `run_cli` executes your Click command it will:
1. Build a signal spec list (custom or default).
2. Optionally install handlers that raise the exceptions above.
3. Execute the command with `standalone_mode=False`.
4. Funnel any exception through `handle_cli_exception`.
5. Restore prior signal handlers and flush streams before returning (or rely on any injected replacements).

This behaviour keeps CLI wiring consistent across projects embedding `lib_cli_exit_tools` while still allowing custom hooks when needed.

### Advanced CLI wiring

For larger applications, keep module execution, console scripts, and shared helpers aligned. The snippet below shows how `__main__.py` can catch unexpected errors and map them through `lib_cli_exit_tools` before exiting:

```python
# src/your_package/__main__.py
from __future__ import annotations

import lib_cli_exit_tools

from .cli import main

if __name__ == "__main__":
    try:
        exit_code = int(main())
    except BaseException as exc:  # fallback to shared exit helpers
        lib_cli_exit_tools.print_exception_message()
        exit_code = lib_cli_exit_tools.get_system_exit_code(exc)
    raise SystemExit(exit_code)
```

A multi-command Click CLI can reuse the same configuration object and expose custom commands while still delegating wiring to `run_cli`:

```python
# src/your_package/cli.py
from __future__ import annotations

from typing import Sequence

import rich_click as click

import lib_cli_exit_tools

from . import __init__conf__
from .lib_template import hello_world as _hello_world
from .lib_template import i_should_fail as _fail

CLICK_CONTEXT_SETTINGS = dict(help_option_names=["-h", "--help"])  # noqa: C408


@click.group(help=__init__conf__.title, context_settings=CLICK_CONTEXT_SETTINGS)
@click.version_option(
    version=__init__conf__.version,
    prog_name=__init__conf__.shell_command,
    message=f"{__init__conf__.shell_command} version {__init__conf__.version}",
)
@click.option(
    "--traceback/--no-traceback",
    is_flag=True,
    default=False,
    help="Show full Python traceback on errors",
)
@click.pass_context
def cli(ctx: click.Context, traceback: bool) -> None:
    """Root CLI group. Stores global opts in context & shared config."""
    ctx.ensure_object(dict)
    ctx.obj["traceback"] = traceback
    lib_cli_exit_tools.config.traceback = traceback


@cli.command("info", context_settings=CLICK_CONTEXT_SETTINGS)
def cli_info() -> None:
    """Print project information."""
    __init__conf__.print_info()


@cli.command("hello", context_settings=CLICK_CONTEXT_SETTINGS)
def cli_hello() -> None:
    """Print the standard hello message."""
    _hello_world()


@cli.command("fail", context_settings=CLICK_CONTEXT_SETTINGS)
def cli_fail() -> None:
    """Trigger the intentional failure helper."""
    _fail()


def main(argv: Sequence[str] | None = None) -> int:
    """Entrypoint returning an exit code via shared run_cli helper."""
    return lib_cli_exit_tools.run_cli(
        cli,
        argv=list(argv) if argv is not None else None,
        prog_name=__init__conf__.shell_command,
    )
```

When installed, your package's console scripts (defined in `pyproject.toml`) will import `your_package.cli:main`, and `python -m your_package` will follow the same code path via `__main__.py`.

## Exit Codes

- SIGINT → 130, SIGTERM → 143 (POSIX), SIGBREAK → 149 (Windows)
- SystemExit(n) → n
- Common exceptions map to POSIX/Windows codes (FileNotFoundError, PermissionError, ValueError, etc.)

### Broken pipe behavior
- Default: exit 141 quietly (128+SIGPIPE), no noisy error output.
- Configure: `config.broken_pipe_exit_code = 0` to treat as benign truncation, or `32` (EPIPE).

### Sysexits mode (optional)
- Set `config.exit_code_style = "sysexits"` to map ValueError/TypeError → EX_USAGE(64),
  FileNotFoundError → EX_NOINPUT(66), PermissionError → EX_NOPERM(77), generic OSError → EX_IOERR(74).

## Modern Python Toolchain

- Targets Python 3.10+ for modern language features and broad compatibility.
- Development extras track the latest stable releases published on PyPI so quality gates match local and CI environments.
- GitHub Actions workflows rely on the current major releases of `actions/checkout`, `actions/setup-python`, and `astral-sh/setup-uv`, aligning the automation stack with the 2025 runner images.

## Additional Documentation

- [INSTALL](INSTALL.md)
- [CHANGELOG](CHANGELOG.md)
- [CONTRIBUTING](CONTRIBUTING.md)
- [DEVELOPMENT](DEVELOPMENT.md)
- [MODULE REFERENCE](docs/system-design/module_reference.md)
- [LICENSE](LICENSE)