env.py

#!/usr/bin/env python
"""

The env_file should have one KEY=VALUE per line and it can include spaces.

If the env_file is a JSON file (filename ends in .json), a list of dictionaries
is expected in the form:

    [ { "name": "KEY", "value": "value" }, ... ]

To pass arguments to the commnd, use --; for example:

    ./env.py <file.env|env.json> ls -- -al

"""

import os
import argparse
import json

def main():

    parser = argparse.ArgumentParser(description="Load ENV variables and run a process.")
    parser.add_argument("--inherit", "-i", dest="inherit",
                        action="store_true", help="Merge the env_file with current ENV")
    parser.add_argument("env_file", help="File with ENV variables (one VAR=VALUE per line, or a JSON file)")
    parser.add_argument("cmd", help="Command to execute")
    parser.add_argument("args", nargs="*", help="Arguments")

    args = parser.parse_args()

    if args.inherit:
        env = os.environ.copy()
    else:
        env = {}

    if args.env_file.endswith(".json"):
        with open(args.env_file, "r") as fd:
            data = json.load(fd)

        for line in data:
            if not "name" in line or not "value" in line:
                parser.error("invalid JSON format in %r" % args.env_file) 
            env[line["name"]] = line["value"]
    else:
        with open(args.env_file, "r") as fd:
            lines = fd.readlines()

        for line in lines:
            line = line.strip()
            if not line:
                continue
            k, v = line.split("=", 1)
            env[k] = v

    os.execvpe(args.cmd, [args.cmd,] + args.args, env)

if __name__ == "__main__":
    main()