Loading env vars in your build scripts

When you are using scripts to automate your builds (which you should do), you most probably want to keep the definition of your environment variables in an external file.

For example, in our builds, we are using multiple versions of Xcode and therefor need to set the proper DEVELOPER_DIR environment variable.

You can store these in a file as follows:

.env

1DEVELOPER_DIR=/Applications/Xcode-v12.1.app/Contents/Developer

If you are using plain shell scripts, loading the variables is easy:

1source .env
2echo $DEVELOPER_DIR

To load them into a Makefile, you can use the following trick:

Makefile

1include .env
2export
3
4build:
5    @echo $(DEVELOPER_DIR)

Since we have some older build scripts which are based on Apache Ant, you can use the same file in Apache Ant by using the loadproperties task:

1<?xml version="1.0" encoding="UTF-8"?>
2<project name="builder" default="init" basedir=".">
3    <target name="init">
4        <loadproperties srcFile=".env" />
5        <echo message="${DEVELOPER_DIR}" />
6    </target>
7</project>

If you want to read them from Python, you can do:

 1import os
 2
 3def read_properties_from_file(path):
 4    return dict(l.rstrip().split('=', maxsplit=1) for l in open(path) if not l.startswith("#"))
 5
 6def load_env_vars_from_properties_file(path):
 7    props = read_properties_from_file(path)
 8    for k, v in props.items():
 9        os.environ[k] = v
10
11def main():
12    load_env_vars_from_properties_file(".env")
13        print(os.environ.get("DEVELOPER_DIR")
14
15if __name__ == '__main__':
16    main()

Voila, a neat way to have all your build scripts share the same environment variables.