node.js - node的child_process.spawn(...[, options])怎么写多个options?

Question

如果有多个grep，怎么写到上面的语句中？例如cat /dev/urandom |od -x|tr -d ' '|head -n 1

在网上找了下，发现用以下的方法也行，使用spawn和exec有什么区别呢？

const exec = require('child_process').exec;
exec('cat /dev/urandom |od -x|tr -d ' '|head -n 1', (error, stdout, stderr) => {
  if (error) {
    console.error(`exec error: ${error}`);
    return;
  }
  console.log(`stdout: ${stdout}`);
  console.log(`stderr: ${stderr}`);
});

Answer 1

如果不封装的话，你需要监听多个事件，举例说cat /dev/urandom |od -x|tr -d ' '|head -n 1

const spawn = require('child_process').spawn;
const cat = spawn('cat', ['/dev/urandom']);
const od = spawn('od',['-x']);
const tr = spawn('tr',['-d'," "]);
const head = spawn('head', ['-n',1]);

cat.stdout.on('data', data => od.stdin.write(data));
cat.on('close', (code) => od.stdin.end());

od.stdout.on('data', data => tr.stdin.write(data));
od.on('close', (code) => tr.stdin.end());

tr.stdout.on('data', data => head.stdin.write(data));
tr.on('close', (code) => head.stdin.end());

head.stdout.on('data', data => console.log(`${data}`));
head.stdin.on('error',err=>head.stdin.end());

也可以在spwan创建子进程的时候制定一下pipe管道，比如这样

const spawn = require('child_process').spawn;
const cat = spawn('cat', ['/dev/urandom'], {stdio: 'pipe'});
const od = spawn('od',['-x'], {stdio: [cat.stdout, 'pipe', 'pipe']});
const tr = spawn('tr',['-d',' '], {stdio: [od.stdout, 'pipe', 'pipe']});
const head = spawn('head', ['-n',1], {stdio: [tr.stdout, 'pipe', 'pipe']});

head.stdout.on('data', data => console.log(`${data}`));
head.stdin.on('error',err=>head.stdin.end());

实际环境下，还要处理stderr那边的信息

Answer 2

你给的例子没有grep呀？

https://nodejs.org/api/child_...

多个options 以数组的形式作为 第二个参数传递： ls -lh /usr

const spawn = require('child_process').spawn;
const ls = spawn('ls', ['-lh', '/usr']);

你给的例子cat /dev/urandom |od -x|tr -d ' '|head -n 1

就照着你截图的那个管道分开做：

// cat /dev/urandom
const cat = spawn('cat',['/dev/urandom']);
//od -x
const od = spawn('od',['-x']);
//tr -d ' '
const tr = spawn('tr', ['-d',"' '"]);
//head -n 1
const head = spwan('head', ['-n','1']);

然后管道的话看你截图那个例子怎么写的咯，就是回调里执行下一个指令的样子