shell-lib 1.2.2

A simple Python utility to simplify the writing of shell-like scripts.

Introduction

shell-lib is designed to simplify the writing of shell-like scripts.

This module was co-created with Google Gemini.

Changelog

Why shell-lib?

• Clean and readable syntax: Write scripts in readable Python, freeing from complex shell command syntax.
• Reliable error handling: Use Python's exception to manage command failure. If a command fails, by default, it raises a subprocess.CalledProcessError exception. For commands that may fail, user can also only check the exit-code.
• Unified file system operations: Provide a consistent and intuitive file system operations API, that clearly distinguish between file and directory operations.
• Cross-platform compatibility: Write a single script that works across Linux, macOS, and Windows platforms.
• Rich ecosystem integration: Easily integrate with both the CLI tool and Python library ecosystems.
• Lightweight and portable: Only use Python standard library.
• Well tested: Consistent behavior on different platforms and Python versions.

Usage

#!/usr/bin/python3
from shell_lib import sh

PROJECT_PATH = "my_project"
FILE = "hello.txt"

# `with sh:` is a *top-level* context manager.
# Its main purpose is, if `sh()` or `sh.safe_run()` fails, return the error
# exit-code from the command. If you don't need this, don't use it.
with sh:
    sh.create_dir(PROJECT_PATH)
    # sh.cd() context manager restores the previous working directory when
    # exiting the code block, even if an exception raised within the code block.
    with sh.cd(PROJECT_PATH):
        sh(f"echo 'Hello, World!' > {FILE}")
        print(f"File size: {sh.get_path_info(FILE).size} bytes")
    sh.remove_dir(PROJECT_PATH)

There is a demo script at the bottom of this page.

API Reference

File and Directory Operations

Path parameters can be str, bytes or pathlib.Path object.

• sh.home_dir() -> Path: Gets the current user's home directory, a pathlib.Path object.

• sh.path(path) -> Path: Converts a str/bytes path to a pathlib.Path object. Can utilize the rich features of pathlib module.

• sh.create_dir(path, *, exist_ok=False): Creates a directory.

• sh.remove_file(path, *, ignore_missing=False): Removes a file.

• sh.remove_dir(path, *, ignore_missing=False): Recursively removes a directory.

• sh.clear_dir(path) -> None: Clear the contents of a directory.

• sh.copy_file(src, dst, *, remove_existing_dst=False): Copies a file.

• sh.copy_dir(src, dst, *, remove_existing_dst=False): Copies a directory.

• sh.move_file(src, dst, *, remove_existing_dst=False): Moves a file.

• sh.move_dir(src, dst, *, remove_existing_dst=False): Moves a directory.

• sh.rename_file(src, dst): Renames a file.

• sh.rename_dir(src, dst): Renames a directory.

• sh.list_dir(path): Lists all entry names within a directory.

• sh.walk_dir(path, top_down=True): A generator that traverses a directory tree, yield a tuple(directory_path, file_name).

• sh.cd(path: str|bytes|Path|None): Changing the working directory. Can be used as a context manager.

• sh.split_path(path): os.path.split() alias.

• sh.join_path(*paths): os.path.join() alias.

• sh.path_exists(path) -> bool: Checks if a path exists.

• sh.is_file(path) -> bool: Checks if a path is a file, or a symlink pointing to a file.

• sh.is_dir(path) -> bool: Checks if a path is a directory, or a symlink pointing to a directory.

• sh.is_link(path) -> bool: Checks if a path is a symlink.

• sh.get_file_size(path) -> int: Get file size.

• sh.get_path_info(path) -> PathInfo: Retrieves detailed information about an existing file or directory:

>>> sh.get_path_info('/usr/bin/')  # directory
PathInfo(path=/usr/bin/, size=69632, ctime=2025-09-16 08:18:21.992288,
mtime=2025-09-16 08:18:21.992288, atime=2025-09-17 09:43:29.210739,
is_dir=True, is_file=False, is_link=False,
is_readable=True, is_writable=False, is_executable=True)

>>> sh.get_path_info('/usr/bin/python3')  # file
PathInfo(path=/usr/bin/python3, size=8021824, ctime=2025-08-29 13:12:47.657879,
mtime=2025-08-15 01:47:21, atime=2025-09-16 15:42:37.201079,
is_dir=False, is_file=True, is_link=True,
is_readable=True, is_writable=False, is_executable=True)

Shell Command Execution

Executes a command with shell=True. Allows shell features like pipe (|) and redirection (>).

sh(command: str, *,
   text: bool = True,
   input: str|bytes|None = None,
   timeout: int|float|None = None,
   alternative_title: str|None = None,
   print_output: bool = True,
   fail_on_error: bool = True) -> subprocess.CompletedProcess

# alternative_title:
#     Print this title instead of the command.
#     Used for commands containing sensitive information.
# print_output:
#     True: streams stdout and stderr to the console.
#     False: stdout and stderr are saved in return value's `stdout`/`stderr` attributes.
# fail_on_error:
#     True: raises a subprocess.CalledProcessError on failure.
#     False: doesn't raise exception, need to check return value's `returncode` attribute
#            to see if it has failed.

Compared with sh() above, it runs with shell=False. It only accepts a list of strings to prevent shell injection. Use this method when the command contains external input.

sh.safe_run(command: list[str], *,
            text: bool = True,
            input: str|bytes|None = None,
            timeout: int|float|None = None,
            alternative_title: str|None = None,
            print_output: bool = True,
            fail_on_error: bool = True) -> subprocess.CompletedProcess

# On Windows, need to use this to run complex PowerShell command:
cmd = "pip freeze | foreach-object { pip install --upgrade $_.split('==')[0] }"
sh.safe_run(['powershell', '-Command', cmd])

User interaction

• sh.ask_choice(title: str, *choices: str) -> int: Displays a menu and gets a 1-based index from the user's choice.
• sh.ask_yes_no(title: str) -> bool: Asks user to answer yes or no.
• sh.ask_regex_input(title: str, pattern: str, *, print_pattern: bool = False) -> re.Match: Ask user to input a string, and verify it with a regex pattern.
• sh.ask_password(title: str = "Please input password") -> str: Ask user to input a password, not echo on screen. No need to add : at the end of title.
• sh.pause(msg: str|None = None) -> None: Prompts the user to press any key to continue.
• sh.exit(exit_code: int = 0): Exits the script with a specified exit code.

Get system information

• sh.get_preferred_encoding() -> str: Get the preferred encoding, used for subprocess output or files that don't specify an encoding.
• sh.get_locale_encoding() -> str: Get the system locale encoding.
• sh.get_filesystem_encoding() -> str: Get the encoding used to convert between str filenames and bytes filenames inside Python.
• sh.get_env(key: str, default: str|None = None) -> Union[str, None]: Get an environment variable.
• sh.set_env(key: str, value: str|None, /) or sh.set_env(dict: Dict[str, str|None], /): Set environment variable(s), None means delete, the changes affect the current process and subprocesses. Can also be used as a context manager for automatically restore.
• sh.get_username() -> str: Get the current username. On Linux, if running a script with sudo -E ./script.py, return root. To get the username in this case, use: sh.home_dir().name
• sh.is_elevated() -> bool: If the script is running with elevated (admin/root) privilege.
• sh.is_os(os_mask: int) -> bool: Test whether it's the OS specified by the parameter.

# os_mask can be:
sh.OS_Windows
sh.OS_Cygwin
sh.OS_Linux
sh.OS_macOS
sh.OS_Unix
sh.OS_Unix_like  # It's (OS_Linux | OS_macOS | OS_Unix | OS_Cygwin)

# Support bit OR (|) combination:
if sh.is_os(sh.OS_Linux | sh.OS_macOS):
    ...
elif sh.is_os(sh.OS_Windows):
    ...

Demo script

#!/usr/bin/python3
import os
from shell_lib import sh
# shell-lib demo script: Build and install cpython on Linux
# Need to install build dependencies first:
# https://devguide.python.org/getting-started/setup-building/#install-dependencies

# Input Python version
m = sh.ask_regex_input('Please input Python version to install (such as 3.13.7)',
                       r'\s*(((\d+)\.(\d+))\.\d+)\s*')
ver = m.group(1)
ver_2 = m.group(2)
ver_info = int(m.group(3)), int(m.group(4))

# Variables
work_dir = sh.home_dir() / 'build_python'
xz_filename = sh.path(f'Python-{ver}.tar.xz')
compile_dir = f'Python-{ver}'
install_dir = sh.path(f'/opt/python{ver_2}')
url = f'https://www.python.org/ftp/python/{ver}/Python-{ver}.tar.xz'

# Check existing installed Python
msg = (f'Install path `{install_dir}` is exsiting, '
       f'overwrite install(yes) or exit(no)?')
if install_dir.is_dir() and not sh.ask_yes_no(msg):
    sh.exit()

# Build options
config = f'./configure --prefix={install_dir}'
optimize = sh.ask_choice('Please choose build options',
                         'PGO + LTO (very slow)',
                         'LTO (slow)',
                         'No optimization',
                         'Debug build')
if optimize == 1:
    config += ' --enable-optimizations --with-lto'
elif optimize == 2:
    config += ' --with-lto'
elif optimize == 3:
    pass
elif optimize == 4:
    config += ' --with-pydebug'

if ver_info >= (3, 13) and sh.ask_yes_no("Build Free-threaded build?"):
    config += ' --disable-gil'

sh.create_dir(work_dir, exist_ok=True)
with sh.cd(work_dir):
    if not xz_filename.is_file() or sh.get_file_size(xz_filename) == 0:
        sh(f'wget --no-proxy -O {xz_filename} {url}')

    password = sh.ask_password('Please input sudo password')
    sh(f'echo {password} | sudo -S rm -rf {compile_dir}',
       alternative_title='Clear building directory')
    sh(f'tar -xvf {xz_filename}', print_output=False)

    with sh.cd(compile_dir):
        # Compile
        with sh.set_env('CFLAGS', '-O2'):
            sh(config, print_output=False)
        sh('make clean')
        sh(f'make -j{os.cpu_count()}')
        sh.pause('Please check for missing modules')

        # Install
        sh(f'echo {password} | sudo -S rm -rf {install_dir}',
           alternative_title='Remove existing install directory')
        sh(f'echo {password} | sudo -S make install',
           alternative_title='Install compiled Python')

    if sh.ask_yes_no('Run unit-tests? (very slow)'):
        sh(f'{install_dir}/bin/python{ver_2} -m test', fail_on_error=False)

    if sh.ask_yes_no('Remove building directory?'):
        sh(f'echo {password} | sudo -S rm -rf {compile_dir}',
           alternative_title='Remove building directory')