Represents a read filehandle that your program can use to read from the command $cmd’s standard output. Can be a filehandle object or a reference to a typeglob.

Represents a write filehandle that your program can use to write to the command $cmd’s standard input. Can be a filehandle object or a reference to a typeglob.

The command to be executed by the child process and its arguments. Can be specified two ways:

$cmd_with_args
$cmd, "arg1", "arg2", ...