This package provides subprocess creation.
define popen(command: String, mode: *String): File
command as a subprocess in
mode. The result of this function is
File that can be read from or written to like any other
The mode provided must be one of the following:
"r"Read mode. This allows reading from the stdout of the subprocess.
"w"Write mode. This allows writing to the stdin of the subprocess.
ValueErrorif mode is not one of the modes listed above.
RuntimeErrorif unable to start the subprocess.