Bash process substitution used as an option value

Question

I'm trying to run

docker-compose --env-file <(cat file1.env <(echo -e "\n\n") file2.env) config

docker-compose expects --env-file to be a file. I need to use (concatenate) two files.

Running docker-compose --env-file file_any.env config works well.

Running cat file1.env <(echo -e "\n\n") file2.env separately outputs valid result.

But it somehow doesn't work with docker-compose.

What am I doing wrong?

Answer 1

You don't need an additional process substitution. The outer process substitution captures the standard output of all the commands it wraps, so you aren't limited to a single cat command.

docker-compose --env-file <( cat file1.env; printf '\n\n'; cat file2.env) config

Unfortunately, docker-compose requires the argument to --env-file be a real file. The value of the argument is passed directly to Environment.from_env_file, which makes an explicit check via env_vars_from_file:

def env_vars_from_file(filename, interpolate=True):
    """
    Read in a line delimited file of environment variables.
    """
    if not os.path.exists(filename):
        raise EnvFileNotFound("Couldn't find env file: {}".format(filename))
    elif not os.path.isfile(filename):
        raise EnvFileNotFound("{} is not a file.".format(filename))
    ...