child.stdio
A sparse array of pipes to the child process, corresponding with positions in the stdio option passed to child_process.spawn() that have been set to the value 'pipe'. Note that child.stdio[0], child.stdio[1], and child.stdio[2] are also available as child.stdin, child.stdout, and child.stderr, respectively.
In the following example, only the child's fd 1 (stdout) is configured as a pipe, so only the parent's child.stdio[1] is a stream, all other values in the array are null.
const assert = require('assert');
const fs = require('fs');
const child_process = require('child_process');
const child = child_process.spawn('ls', {
stdio: [
0, // Use parents stdin for child
'pipe', // Pipe child's stdout to parent
fs.openSync('err.out', 'w') // Direct child's stderr to a file
]
});
assert.equal(child.stdio[0], null);
assert.equal(child.stdio[0], child.stdin);
assert(child.stdout);
assert.equal(child.stdio[1], child.stdout);
assert.equal(child.stdio[2], null);
assert.equal(child.stdio[2], child.stderr);
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