Python tool to make long CLI commands interactive

nutshell.py

#! /usr/bin/env python
'''
Nutshell - make long CLI commands interactive
---------------------------------------------

I am lazy. I am forgetful. I often have to write long CLI commands.

The shell history does an awesome job of remembering them for me but too often
I end up working too hard in trying to find the line I wrote a couple of days
back and having to change something simlple e.g. name of a file etc.

With Nutshell I am trying to make a sidekick for alias. At its simplest:

    $ python nutshell.py 'hadoop fs -cat hdfs:///#project/#package/#file | head -n#lines'
    'project' > my-project
    'package' > my-package
    'file' > data.csv
    'lines' > 5
    <Runs hadoop fs -cat hdfs:///my-project/my-package/data.csv | head -n5>
    ...
    
You can set environment variables starting with `NUTSHELL_` to pass in arguments like so:
    
    $ export NUTSHELL_lines=10
    $ python nutshell.py 'hadoop fs -cat hdfs:///#project/#package/#file | head -n#lines'
    'project' > my-project
    'package' > my-package
    'file' > data.csv
    <Runs hadoop fs -cat hdfs:///my-project/my-package/data.csv | head -n10>
    ...

You can also pass in CLI arguments - useful for having your shell history just so:

    $ export NUTSHELL_lines=10
    $ python nutshell.py 'hadoop fs -cat hdfs:///#project/#package/#file | head -n#lines' #file='foo.csv'
    'project' > my-project
    'package' > my-package
    <Runs hadoop fs -cat hdfs:///my-project/my-package/foo.csv | head -n10>
    ...

Finally, CLI arguments override environment variables:

    $ export NUTSHELL_lines=10
    $ python nutshell.py 'hadoop fs -cat hdfs:///#project/#package/#file | head -n#lines' #lines='8'
    'project' > my-project
    'package' > my-package
    'file' > data.csv
    <Runs hadoop fs -cat hdfs:///my-project/my-package/foo.csv | head -n8>
    ...

Enjoy!
'''

import os
import sys
from subprocess import Popen, PIPE, STDOUT
from string import Template


def _stdin23(prompt):
    '''Takes input from user. Works for Python 2 and 3.'''
    _v = sys.version[0]
    return input(prompt) if _v is '3' else raw_input(prompt)


def env(env=None, prefix='NUTSHELL_'):
    '''Reads env variables like NUTSHELL_<var_name>, parse
    them and returns a dict.
    >>> env_overrides(env={'yo': 0, 'A_yo': 1}, pre='A_')
    {'yo': 1}
    '''
    env = env or os.environ
    _vars = env.iteritems()
    for k, v in env.iteritems():
        if k.startswith(prefix):
            yield (k.lstrip(prefix), v)


def cli(args=None, prefix='#'):
    '''Reads cli overrides like #<var_name>=<value>.'''
    args = args or sys.argv[1:]
    for arg in args:
        if arg.startswith(prefix):
            k, v = arg.split('=')
            yield (k.lstrip(prefix), v)


class Nutshell(object):

    def __init__(self, args, prefix='#', _input=_stdin23):
        self.cmd = args[0]
        self.overrides = args[1:]
        self.prefix = prefix
        self._input = _input
        self.tpl_class = type("NutTpl", (Template,), {'delimiter': '#'})

    def render(self, overrides):
        '''Tries to render template, fails by asking questions
        if no overrides found.'''
        tpl = self.tpl_class(self.cmd)
        data = overrides or {}
        while True:
            try:
                return tpl.substitute(**data)
            except KeyError as e:
                ans = str(self._input('%s > ' % e))
                data.update({e.message: ans})

    def run(self):
        overrides = dict(list(env()) + list(cli()))
        cmd = self.render(overrides)
        print cmd
        p = Popen(cmd, shell=True, stdout=PIPE, stderr=STDOUT)
        p.wait()
        return p.stdout.read().strip()

if __name__ == '__main__':
    print Nutshell(sys.argv[1:]).run()