I am using the Node FFI module and am trying to run sync tasks on Windows. I can successfully run a task using the following code.
var ffi=require('ffi')
var nativeC = new ffi.Library("Kernel32", {
"WinExec": ["int32", ["string"]]
});
nativeC.WinExec('ls -lrt');
I presume this is the way to execute sync tasks, but this code always exits after the 1st 'ls -lrt' command; if I chain a few more commands, they won't work. So, is there a callback function over here, in the FFI module, or another way I can chain commands in node.js on Windows so they run in sync, one after the other.
I'm not sure you need WinExec to run a windows command. As Jonathan pointed out, ls isn't available.
However, if you want to chain commands you could use async.js and exec like this:
var
async = require('async');
exec = require('child_process').exec,
commands = [ 'dir /w', 'echo test'];
var executeCommand = function(command, callback){
exec(command, function (err, stdout, stderr) {
if(err) return callback(err);
console.log(stdout);
callback();
});
};
async.eachSeries(commands, executeCommand, function(err){
console.log('error: ' + err);
});
Related
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());
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.
Hi can anyone help me with a custom grunt task?
I'm basically using child_process to call
var cp = exec(cmd, {}, function (err, stdout, stderr) {}
this of course has the stdout etc. If I
cp.stdout.pipe(process.stdout);
it rights a bunch of stuff to the console. I am making this call in a loop so here's a skeleton
this.files.forEach(function(f) {
var src = f.src.map(function(filepath) {
var cmd = util.format("%s %s", options.xUnit, src);
var cp = exec(cmd, {}, function (err, stdout, stderr) {
....
cb();
});
if (options.stdout || grunt.option('verbose')) {
cp.stdout.pipe(process.stdout);
}
This all works fine. but since I'm doing it several times I want at the very least to be able to index how many times stderr has a value. I'm basically running collections of tests. If all pass then stderr is blank if not, I don't want to stop the rest of the tests I want them all to run, but i'd like to output at the end "you have 3 collections that have failing tests". I don't see why I can't seem to get it to work. If I declare
var output = 0;
then
if (options.stderr || grunt.option('verbose')) {
cp.stdout.pipe(process.stdout);
output ++;
}
I then try to print to console after they all run but it's always 0.
I would really like to some how get a copy of ALL the output and parse out the last line from each test session which has the number of tests that failed in it. But that just seems way out of realm of possiblity. I've tried all manner of stuff with the streams and got less than nothing.
Anyway, if anyone can help I would greatly appreciate it
Am using bellow code to pass two arguments along with an exe file execution as follows.But it is not working.in command line it is working properly.
var osName =jobData[0].os;
exec('Shedule.exe',['value=Start'],['ID=osName'], function (err, data) {
console.log(data);
});
in cmd
C:\Users\Desktop\ver>Shedule.exe value=Start ID=WIN7-64
Try this.I think this will solve your problem.
var osName =jobData[0].os;
exec('Shedule.exe',['value=Start','ID='+osName], function (err, data) {
console.log(data);
});
I am trying to run a command inside a async.forEach loop using ChildProcess.exec in my node job. here is the code
async.forEach( docPaths, function(docPath, callback) {
var run = [];
// some command using docPath variable here..
run.push(command);
debugger;
exec(run.join(' '), function(error, stdout, stderr){
callback();
});
}, callback);
Here is the error
"stack":"Error: spawn EMFILE\
at errnoException (child_process.js:478:11)\
at ChildProcess.spawn (child_process.js:445:11)\
at child_process.js:343:9\
at Object.execFile (child_process.js:253:15)\
at child_process.js:220:18\
a quick google shows i need to set ulimit value to increase the number of file descriptors can be open. some thing like "ulimit -n 10000".. (from link below)
https://groups.google.com/forum/#!topic/nodejs/jeec5pAqhps
where can i increase this..? or is there any other solution to circumvent the issue?
Appreciate your help.. Thanks much !!
First of all its not advisable to mess with ulimit, as it may have system wide impacts.
Instead since you are already using async, it comes with a limit paramater which you can use to limit the number of parallely executions.
async.eachLimit( docPaths, 100, function(docPath, callback) {
var run = [];
// some command using docPath variable here..
run.push(command);
debugger;
exec(run.join(' '), function(error, stdout, stderr){
callback();
});
}, callback);
Please do trial and error and replace 100 with suitable value.
Is it possible to execute an external program from within node.js? Is there an equivalent to Python's os.system() or any library that adds this functionality?
var exec = require('child_process').exec;
exec('pwd', function callback(error, stdout, stderr) {
// result
});
exec has memory limitation of buffer size of 512k. In this case it is better to use spawn.
With spawn one has access to stdout of executed command at run time
var spawn = require('child_process').spawn;
var prc = spawn('java', ['-jar', '-Xmx512M', '-Dfile.encoding=utf8', 'script/importlistings.jar']);
//noinspection JSUnresolvedFunction
prc.stdout.setEncoding('utf8');
prc.stdout.on('data', function (data) {
var str = data.toString()
var lines = str.split(/(\r?\n)/g);
console.log(lines.join(""));
});
prc.on('close', function (code) {
console.log('process exit code ' + code);
});
The simplest way is:
const { exec } = require("child_process")
exec('yourApp').unref()
unref is necessary to end your process without waiting for "yourApp"
Here are the exec docs
From the Node.js documentation:
Node provides a tri-directional popen(3) facility through the ChildProcess class.
See http://nodejs.org/docs/v0.4.6/api/child_processes.html