Node.js 同步 shell exec

Question

I am having a problem with async shell executes in node.js.

In my case, node.js is installed on a Linux operating system on a raspberry pi. I want to fill an array with values that are parsed from a shell script which is called on the pi. This works fine, however, the exec() function is called asynchronously.

I need the function to be absolute synchron to avoid messing up my whole system. Is there any way to achieve this? Currently I am trying a lib called .exe, but the code still seems to behave asynchron.

Here's my code:

function execute(cmd, cb)
{
  child = exec(cmd, function(error, stdout, stderr)
  {
    cb(stdout, stderr);
  });
}



function chooseGroup()
{
  var groups = [];

  execute("bash /home/pi/scripts/group_show.sh", function(stdout, stderr)
  {
    groups_str  = stdout;
    groups      = groups_str.split("\n");
  });

  return groups;
}


//Test
console.log(chooseGroup());

Answer 1

If what you're using is child_process.exec , it is asynchronous already.

Your chooseGroup() function will not work properly because it is asynchronous. The groups variable will always be empty.

Your chooseGroup() function can work if you change it like this:

function chooseGroup() {    
  execute("bash /home/pi/scripts/group_show.sh", function(stdout, stderr) {
    var groups = stdout.split("\n");
    // put the code here that uses groups
    console.log(groups);
  });
}

// you cannot use groups here because the result is obtained asynchronously
// and thus is not yet available here.

If, for some reason, you're looking for a synchronous version of .exec() , there is child_process.execSync() though it is rarely recommended in server-based code because it is blocking and thus blocks execution of other things in node.js while it is running.