The evergreen documentation encourages using subprocess.exec rather than shell.exec to run scripts. In my experience, subprocess.exec makes it much easier to determine which values are defined in an environment. It also encourages the use of external script files over inlined bash, which can help to avoid some of the trickiness that comes with distinguishing between expansions and environment variables. We should port our config file to use subprocess.exec and avoid future usage of shell.exec.

https://docs.devprod.prod.corp.mongodb.com/evergreen/Project-Configuration/Best-Practices