Error running example code in a serialized loop - node.js

Question

I have been tinkering around with node a little, and while trying to learn the child_process module, I ran into a problem. I was attempting to serialize many calls to 'ps -eF | grep ssh', but it crashes on my system with the error below. So two questions. First, is there a better way to do what I am attempting without a library? Second, why isn't it working :)
events.js:71
throw arguments[1]; // Unhandled 'error' event
^
Error: This socket is closed.
at Socket._write (net.js:519:19)
at Socket.write (net.js:511:15)
at Socket.<anonymous> (/home/me/tmp/test.js:10:16)
at Socket.EventEmitter.emit (events.js:96:17)
at Pipe.onread (net.js:397:14)
function callpsgrep(callback) {
var spawn = require('child_process').spawn,
ps = spawn('ls', ['-la']),
grep = spawn('grep', ['bananas']);
ps.stdout.on('data', function (data) {
grep.stdin.write(data);
});
ps.stderr.on('data', function (data) {
console.log('ps stderr: ' + data);
});
ps.on('exit', function (code) {
if (code !== 0) {
console.log('ps process exited with code ' + code);
}
grep.stdin.end();
});
grep.stdout.on('data', function (data) {
console.log('' + data);
});
grep.stderr.on('data', function (data) {
console.log('grep stderr: ' + data);
});
grep.on('exit', function (code) {
if (code !== 0) {
console.log('grep process exited with code ' + code);
}
callback();
});
}
function series(i) {
if (i < 1000) {
callpsgrep( function() {
return series(i+1);
});
}
}
series(0);

Answer 1

Close grep's stdin on the close event instead of the exit event.
ps.on('exit', function (code) {
if (code !== 0) {
console.log('ps process exited with code ' + code);
}
});
ps.on('close', function (code) {
grep.stdin.end();
});
Although not very well documented I read the following in the help file.
Event: 'exit'
Note that the child process stdio streams might still be open.
Event: 'close'#
This event is emitted when the stdio streams of a child process have all terminated. This is distinct from 'exit', since multiple processes might share the same stdio streams.