Per the evergreen docs subprocess.exec is preferred over shell.exec the main reason is that by default it uses bash.

This is notable as nearly every usage in the evergreen.yml file manually specifies shell: bash. While not just a way to save a some lines of yaml file, a task was missing shell: bash and as a result not correct picking up the prepare test env parameters. The task would not fail but log the following errors, hiding the issue:

[2025/10/23 12:23:22.984] sh: 16: [[: not found
[2025/10/23 12:23:22.984] sh: 20: [[: not found
[2025/10/23 12:23:22.984] sh: 23: [[: not found
[2025/10/23 12:23:22.984] sh: 26: [[: not found