ents. `flags` is a keyword that modifies how the program will execute.
* :e - enables passing an environment to the program. Without :e, the current environment is inherited.
* :p - allows searching the current PATH for the binary to execute. Without this flag, binaries must use absolute paths.
* :x - raise error if exit code is non-zero.
* :d - Don't try and terminate the process on garbage collection (allow spawning zombies).
`env` is a table or struct mapping environment variables to values. It can also 