I have set up a command line node module and when I run it one of the tasks is to start up the server and log to the console. However I find that although it starts up my server fine, it does not send the output to the console.
#! /usr/bin/env node
var userArgs = process.argv.slice(2);
var searchPattern = userArgs[0];
if(userArgs[0] === "start"){
var exec = require('child_process').exec;
exec('node ./server.js',
function(err, stdout, stderr) {
console.log('stdout: ', stdout);
console.log('stderr: ', stderr);
if (error !== null) {
console.log('exec error: ', error);
}
}
);
}
So if I npm link my module then run mymodule start it starts the server fine but as I mentioned no output to the console.
Whereas if I run simply node server.js I get the output which is server listening on http://localhost:5000.
From the documentation, regarding the callback you are passing to 'exec'
'callback' - Function called with the output when process terminates
From what I understand, the process has to be terminated before you see 'stdout:' and 'stderr:' (you would have to stop the node process).
Related
I am trying to execute a nodejs file called create-MySwitch.js through a child process in my main.js file.
this is the code for main.js
const exec = require('child_process').exec;
var cmdStr = 'node /home/pi/Desktop/lan-device/create-MySwitch.js';
exec(cmdStr,
{argv: {
port:8080,
uuid:'MyThing'
}},
(error, stdout, stderr)=>{
if (error) {
console.error('exec error: ${error}');
console.log(error);
return;
}
console.log('stdout: ${stdout}');
console.log('stderr: ${stderr}');
});
This is how I am attempting to access the arguments in the create-MySwitch.js file
var port_value = process.argv.port;
var uuid_value = process.argv.uuid;
The output is
stdout: ${stdout}
stderr: ${stderr}
when I run the command
node main.js
I do not think it's working because the output from executing the create-MySwitch.js file should be 'ready', but clearly is not being printed in the stdout variable from the child process.
Essentially, what I am trying to do is run the command 'node createMySwitch.js ', but instead of just typing this in to the command prompt I want to run that command using a child process.
I am doing all of this using the raspbian operating system.
I have created a nw.js desktop application. My requirement is to read data from HID devices. So am using node-hid module. I have written code specific to read and parsing data in usbreader.js file.
In my main.html file am trying to execute node command like below:
exec = require('child_process').exec;
exec('node usbreader.js', function(error, stdout, stderr) {
if (error !== null) {
console.log(stderr);
}
else{
console.log(stdout);
}
});
But am getting error saying:
'node' is not recognized as an internal or external command, operable
program or batch file.
Please help me how can I execute this node js file from nw application
If your usbreader is compatible with your nwjs node version, then you can use it in next way:
usbreader = require('usbreader');
If you want to run it in separate process in node, then you need to install node for your OS. And code is next;
exec = require('child_process').exec;
var usbreaderProc = exec('node usbreader.js', { cwd: '/path/to/usbreader/dir' } function(error, stdout, stderr) {
if (error !== null) {
console.log(stderr);
}
else{
console.log(stdout);
}
});
For the last few days I have been struggling with running shell commands from CasperJS/PhantomJS.
I am running simple unix sed on a file in node, which runs just fine:
var sys = require('sys')
var exec = require('child_process').exec;
var child;
// executes `sed`
child = exec("sed -i -e '1,1000d' file.name", function (error, stdout, stderr) {
sys.print('stdout: ' + stdout);
sys.print('stderr: ' + stderr);
if (error !== null) {
console.log('exec error: ' + error);
}
});
But whenever I run same with CasperJS, it just runs forever, not executing the shell command. Maybe someone could shed some light on this.
I did actually make it work through spawn and execFile functions from PhatomJS, but the issue is that it does not work with large files over 300MB.
How can I run a command line and get the outputs as soon as available to show them somewhere.
For example if a run ping command on a linux system, it will never stop, now is it possible to get the responses while the command is still processing ?
Or let's take apt-get install command, what if i want to show the progress of the installation as it is running ?
Actually i'm using this function to execute command line and get outputs, but the function will not return until the command line ends, so if i run a ping command it will never return!
var sys = require('sys'),
exec = require('child_process').exec;
function getOutput(command,callback){
exec(
command,
(
function(){
return function(err,data,stderr){
callback(data);
}
}
)(callback)
);
}
Try using spawn instead of exec, then you can tap into the stream and listen to the data and end events.
var process = require('child_process');
var cmd = process.spawn(command);
cmd.stdout.on('data', function(output){
console.log(output.toString()):
});
cmd.on('close', function(){
console.log('Finished');
});
//Error handling
cmd.stderr.on('data', function(err){
console.log(err);
});
See the Node.js documentation for spawn here: https://nodejs.org/api/child_process.html#child_process_child_process_spawn_command_args_options
How would I respond to a command line prompt programmatically with node.js? For example, if I do process.stdin.write('sudo ls'); The command line will prompt for a password. Is there an event for 'prompt?'
Also, how do I know when something like process.stdin.write('npm install') is complete?
I'd like to use this to make file edits (needed to stage my app), deploy to my server, and reverse those file edits (needed for eventually deploying to production).
Any help would rock!
You'll want to use child_process.exec() to do this rather than writing the command to stdin.
var sys = require('sys'),
exec = require('child_process').exec;
// execute the 'sudo ls' command with a callback function
exec('sudo ls', function(error, stdout, stderr){
if (!error) {
// print the output
sys.puts(stdout);
} else {
// handle error
}
});
For the npm install one you might be better off with child_process.spawn() which will let you attach an event listener to run when the process exits. You could do the following:
var spawn = require('child_process').spawn;
// run 'npm' command with argument 'install'
// storing the process in variable npmInstall
var npmInstall = spawn('npm', ['install'], {
cwd: process.cwd(),
stdio: 'inherit'
});
// listen for the 'exit' event
// which fires when the process exits
npmInstall.on('exit', function(code, signal) {
if (code === 0) {
// process completed successfully
} else {
// handle error
}
});