How to get environment from a subprocess?

Here's an example of how you can extract environment variables from a batch or cmd file without creating a wrapper script. Enjoy.

from __future__ import print_function
import sys
import subprocess
import itertools

def validate_pair(ob):
    try:
        if not (len(ob) == 2):
            print("Unexpected result:", ob, file=sys.stderr)
            raise ValueError
    except:
        return False
    return True

def consume(iter):
    try:
        while True: next(iter)
    except StopIteration:
        pass

def get_environment_from_batch_command(env_cmd, initial=None):
    """
    Take a command (either a single command or list of arguments)
    and return the environment created after running that command.
    Note that if the command must be a batch file or .cmd file, or the
    changes to the environment will not be captured.

    If initial is supplied, it is used as the initial environment passed
    to the child process.
    """
    if not isinstance(env_cmd, (list, tuple)):
        env_cmd = [env_cmd]
    # construct the command that will alter the environment
    env_cmd = subprocess.list2cmdline(env_cmd)
    # create a tag so we can tell in the output when the proc is done
    tag = 'Done running command'
    # construct a cmd.exe command to do accomplish this
    cmd = 'cmd.exe /s /c "{env_cmd} && echo "{tag}" && set"'.format(**vars())
    # launch the process
    proc = subprocess.Popen(cmd, stdout=subprocess.PIPE, env=initial)
    # parse the output sent to stdout
    lines = proc.stdout
    # consume whatever output occurs until the tag is reached
    consume(itertools.takewhile(lambda l: tag not in l, lines))
    # define a way to handle each KEY=VALUE line
    handle_line = lambda l: l.rstrip().split('=',1)
    # parse key/values into pairs
    pairs = map(handle_line, lines)
    # make sure the pairs are valid
    valid_pairs = filter(validate_pair, pairs)
    # construct a dictionary of the pairs
    result = dict(valid_pairs)
    # let the process finish
    proc.communicate()
    return result

So to answer your question, you would create a .py file that does the following:

env = get_environment_from_batch_command('proc1')
subprocess.Popen('proc2', env=env)

Since you're apparently in Windows, you need a Windows answer.

Create a wrapper batch file, eg. "run_program.bat", and run both programs:

@echo off
call proc1.bat
proc2

The script will run and set its environment variables. Both scripts run in the same interpreter (cmd.exe instance), so the variables prog1.bat sets will be set when prog2 is executed.

Not terribly pretty, but it'll work.

(Unix people, you can do the same thing in a bash script: "source file.sh".)

As you say, processes don't share the environment - so what you literally ask is not possible, not only in Python, but with any programming language.

What you can do is to put the environment variables in a file, or in a pipe, and either

• have the parent process read them, and pass them to proc2 before proc2 is created, or
• have proc2 read them, and set them locally

The latter would require cooperation from proc2; the former requires that the variables become known before proc2 is started.