The stdio option is an array where each index corresponds to a fd in the child.
The value is one of the following:
* 'pipe' - Create a pipe between the child process and the parent process.
The parent end of the pipe is exposed to the parent as a property on the child_process object as ChildProcess.stdio[fd].
Pipes created for fds 0 - 2 are also available as ChildProcess.stdin, ChildProcess.stdout and ChildProcess.stderr, respectively.
* 'ipc' - Create an IPC channel for passing messages/file descriptors between parent and child.
A ChildProcess may have at most one IPC stdio file descriptor. Setting this option enables the ChildProcess.send() method.
If the child writes JSON messages to this file descriptor, then this will trigger ChildProcess.on('message').
If the child is a Node.js program, then the presence of an IPC channel will enable process.send() and process.on('message').
* 'ignore' - Do not set this file descriptor in the child. Note that Node will always open fd 0 - 2 for the processes it spawns.
When any of these is ignored node will open /dev/null and attach it to the child's fd.
* Stream object - Share a readable or writable stream that refers to a tty, file, socket, or a pipe with the child process.
The stream's underlying file descriptor is duplicated in the child process to the fd that corresponds to the index
in the stdio array. Note that the stream must have an underlying descriptor (file streams do not until the 'open'
event has occurred).
* Positive integer - The integer value is interpreted as a file descriptor that is is currently open in the parent process.
It is shared with the child process, similar to how Stream objects can be shared.
* null - Use default value. For stdio fds 0, 1 and 2 (in other words, stdin, stdout, and stderr) a pipe is created.
For fd 3 and up, the default is 'ignore'.
As a shorthand, the stdio argument may also be one of the following strings, rather than an array:
ignore - ['ignore', 'ignore', 'ignore']
pipe - ['pipe', 'pipe', 'pipe']
inherit - [process.stdin, process.stdout, process.stderr] or [0,1,2]