Node JS: Executing command lines and getting outputs asynchronously

Question

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. — Ben Fortune
– Ben Fortune, Commented May 7, 2014 at 11:46
Thanks for you answer, i'm not very familiar with node, just starting whit it, so a little code example, will be very helpful — Xsmael
– Xsmael, Commented May 7, 2014 at 11:46

fatal_error · Accepted Answer · 2018-10-30 07:54:02Z

6

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

edited Oct 30, 2018 at 7:54

fatal_error

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answered May 7, 2014 at 11:45

Ben Fortune

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4 Comments

Xsmael Over a year ago

how does it handling error, i added a listener on cmd.stdout.on('error',... and i want to do so with process object, but process.on(... is not working.

Ben Fortune Over a year ago

For error handling you need to listen on stderr. I've added it into my example. You can't add a listener to process, you need to add it to the spawn.

Xsmael Over a year ago

even with that, i'm still getting an Unhandled 'error' Event while executing a ping command for a test

node server.js <Buffer 65 78 65 63 76 70 28 29 3a 20 4e 6f 20 73 75 63 68 20 66 69 6c 65 20 6f 72 20 64 69 72 65 63 74 6f 72 79 0a> Finished  events.js:72         throw er; // Unhandled 'error' event               ^ Error: spawn ENOENT     at errnoException (child_process.js:988:11)     at Process.ChildProcess._handle.onexit (child_process.js:779:34)

fatal_error Over a year ago

@Xsmael you need to just enter your args as a list, for example: var cmd = process.spawn('ping', ['1.1.1.1']) You can use a shell lexer (like libraries.io/npm/shlex ) to do this for you if you're not sure what your args will look like (ie, if you're writing a wrapper and need to be concerned with spaces.) Also note the security concerns in the documentation link.

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