Plumbum: Shell Combinators

Ever wished the compactness of shell scripts be put into a real programming language? Say hello to Plumbum Shell Combinators. Plumbum (Latin for lead, which was used to create pipes back in the day) is a small yet feature-rich library for shell script-like programs in Python. The motto of the library is "Never write shell scripts again", and thus it attempts to mimic the shell syntax ("shell combinators") where it makes sense, while keeping it all Pythonic and cross-platform.

Apart from shell-like syntax and handy shortcuts, the library provides local and remote command execution (over SSH), local and remote file-system paths, easy working-directory and environment manipulation, and a programmatic Command-Line Interface (CLI) application toolkit. Now let's see some code!

This is only a teaser; the full documentation can be found at Read the Docs

Cheat Sheet

Basics

>>> from plumbum import local
>>> local.cmd.ls
LocalCommand(/bin/ls)
>>> local.cmd.ls()
'build.py\nCHANGELOG.rst\nconda.recipe\nCONTRIBUTING.rst\ndocs\nexamples\nexperiments\nLICENSE\nMANIFEST.in\nPipfile\nplumbum\nplumbum.egg-info\npytest.ini\nREADME.rst\nsetup.cfg\nsetup.py\ntests\ntranslations.py\n'
>>> notepad = local["c:\\windows\\notepad.exe"]
>>> notepad()                                   # Notepad window pops up
''                                              # Notepad window is closed by user, command returns

In the example above, you can use local["ls"] if you have an unusually named executable or a full path to an executable. The local object represents your local machine. As you'll see, Plumbum also provides remote machines that use the same API! You can also use from plumbum.cmd import ls as well for accessing programs in the PATH.

Piping

>>> from plumbum.cmd import ls, grep, wc
>>> chain = ls["-a"] | grep["-v", r"\.py"] | wc["-l"]
>>> print(chain)
/bin/ls -a | /bin/grep -v '\.py' | /usr/bin/wc -l
>>> chain()
'27\n'

Redirection

>>> from plumbum.cmd import cat, head
>>> ((cat < "setup.py") | head["-n", 4])()
'#!/usr/bin/env python3\nimport os\n\ntry:\n'
>>> (ls["-a"] > "file.list")()
''
>>> (cat["file.list"] | wc["-l"])()
'31\n'

Working-directory manipulation

>>> local.cwd
<LocalWorkdir /home/tomer/workspace/plumbum>
>>> with local.cwd(local.cwd / "docs"):
...     chain()
...
'22\n'

Foreground and background execution

>>> from plumbum import FG, BG
>>> (ls["-a"] | grep[r"\.py"]) & FG         # The output is printed to stdout directly
build.py
setup.py
translations.py
>>> (ls["-a"] | grep[r"\.py"]) & BG         # The process runs "in the background"
<Future ['/bin/grep', '\\.py'] (running)>

Command nesting

>>> from plumbum.cmd import sudo, ifconfig
>>> print(sudo[ifconfig["-a"]])
/usr/bin/sudo /sbin/ifconfig -a
>>> (sudo[ifconfig["-a"]] | grep["-i", "loop"]) & FG
lo        Link encap:Local Loopback
          UP LOOPBACK RUNNING  MTU:16436  Metric:1

Remote commands (over SSH)

Supports openSSH-compatible clients, PuTTY (on Windows) and Paramiko (a pure-Python implementation of SSH2)

>>> from plumbum import SshMachine
>>> remote = SshMachine("somehost", user = "john", keyfile = "/path/to/idrsa")
>>> r_ls = remote["ls"]
>>> with remote.cwd("/lib"):
...     (r_ls | grep["0.so.0"])()
...
'libusb-1.0.so.0\nlibusb-1.0.so.0.0.0\n'

CLI applications

import logging
from plumbum import cli

class MyCompiler(cli.Application):
    verbose = cli.Flag(["-v", "--verbose"], help = "Enable verbose mode")
    include_dirs = cli.SwitchAttr("-I", list = True, help = "Specify include directories")

    @cli.switch("--loglevel", int)
    def set_log_level(self, level):
        """Sets the log-level of the logger"""
        logging.root.setLevel(level)

    def main(self, *srcfiles):
        print("Verbose:", self.verbose)
        print("Include dirs:", self.include_dirs)
        print("Compiling:", srcfiles)

if __name__ == "__main__":
    MyCompiler.run()

Sample output

$ python3 simple_cli.py -v -I foo/bar -Ispam/eggs x.cpp y.cpp z.cpp
Verbose: True
Include dirs: ['foo/bar', 'spam/eggs']
Compiling: ('x.cpp', 'y.cpp', 'z.cpp')

Colors and Styles

from plumbum import colors
with colors.red:
    print("This library provides safe, flexible color access.")
    print(colors.bold | "(and styles in general)", "are easy!")
print("The simple 16 colors or",
      colors.orchid & colors.underline | '256 named colors,',
      colors.rgb(18, 146, 64) | "or full rgb colors",
      'can be used.')
print("Unsafe " + colors.bg.dark_khaki + "color access" + colors.bg.reset + " is available too.")