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

如果不封裝的話，你需要監聽多個事件，舉例說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創建子進程的時候制定pipe管道，例如這樣

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());

實際環境下，還要處理stderr那邊的資訊

Answer 2

你給的例子沒有grep呀？

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

多個options 以陣列的形式作為 第二個參數傳遞： ls -lh /usr

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

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

就照著你截圖的那個管道分開做：

// 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']);

然後管道的話看你截圖那個例子怎麼寫的咯，就是回調裡執行下一個指令的樣子