我有 nodejs 子进程的执行流程问题

Question

我想做一个 function 接收作为输入的字符串并将 output 作为字符串返回给我，但由于响应延迟，我无法做到

var resultado = "old value";

function execShell(cmd) {

exec("uname", (error, data, getter) => {
  if(error){
    console.log("error",error.message);
    return;
  }
  if(getter){
    console.log("data",data);
    return;
  }
  console.log(`need before exec: ${data}`);
  resultado = data;

});
}

/* shell command for Linux */

execShell('uname');

console.log(`need after exec: ${resultado}`);

Answer 1

这里发生的是，回调不是从上到下执行的。 这意味着console.log(need after exec: ${resultado}); 在execShell之后直接调用，子进程还没有返回。

您可以使用同步版本来执行它：

const cp = require("child_process");
const result = cp.execSync("uname").toString(); // the .toString() is here to convert from the buffer to a string
console.log(`result after exec ${result}`);

文档是https://nodejs.org/dist/latest-v14.x/docs/api/child_process.html#child_process_child_process_execsync_command_options

You could use a NPM package that helps with the shell handling if that's what you are building: https://github.com/shelljs/shelljs which wraps alot of the child process parts with an easier API.