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Deferred based tool to run exec commands. Lets you use exec, execFile and spawn in a sane way.

Version: 0.3.1


Install the module with: npm install deferred-exec or add it to your project's package.json file.

You can also clone this repo and npm install folderOfClonedRepo to get a branch or development copy.


All calls return a promise, which means it's easy to do stuff when they complete or fail:

var dexec = require( 'deferred-exec' );
dexec( 'echo "yay"' )
  .done( function( stdout, stderr, command ) {
    console.log( stdout ); // logs "yay" 
  .fail( function( error ) {
    console.log( "it didn't work :( got code:", error.code );

Since they are deferreds, you can pass them around in your code:

var dexec = require( 'deferred-exec' );
var command = dexec( 'echo "gotcha"' );
doSomethingWithCommand( command );
// meanwhile, in some other part of your application 
function doSomethingWithCommand( command ) {
  command.done( function( stdout, stderr, command ) {
    console.log( 'just ran', command, 'and got', stdout );

Use Underscore.Deferred if you want to use _.when to group multiple commands. (Note: you can use underscore.deferred with lodash)

var dexec = require( 'deferred-exec' );
// require and mixin lodash with _.deferred 
var _ = require( 'lodash' );
_.mixin( require( 'underscore.deferred' ) );
var commandA = dexec( 'ls /etc' );
var commandB = dexec( 'echo "hi"' );
// when both commands succeed 
_.when( commandA, commandB )
  .done( function( a, b ){
    console.log( 'commandA output:', a[0] );
    console.log( 'commandB output:', b[0] );

Or run a file using .file

var dexec = require( 'deferred-exec' );
dexec.file( './' )
  .done( function( stdout, stderr, fileName ) {
    console.log( 'ran', fileName, 'got', stdout );

Or take advantage of spawning a new progress and getting its output during execution:

var dexec = require( 'deferred-exec' );
dexec.spawn( 'cat', [ '/var/log/syslog' ] )
  .progress( function( stdout, stderr, command ) {
    /* this function will get called with every piece of 
       data from the returne result */
   .done( function( stdout, stderr, command ) {
     /* all done! total value's available of course */


For deferred-exec details see child_process.exec for available options

For deferred-exec.file details see child_process.execFile for available options

For deferred-exec.spawn details see child_progress.spawn for available options


All methods support an options object. deferred-exec adds two possible options to this object:


This defaults to true, which trims the last bit of trailing while space (a new line) from the output. Set to false if you don't want your final output trimmed.


The default is utf8, so if you want one of the other types supported you can specify it here.

API Quick Reference

Assuming `var dexec = require( 'deferred-exec' ):

dexec( String command, Object options )

dexec.execFile( String filename, Array arguments, Object options )

dexec.spawn( String command, Array arguments, Object options )

All methods return a promise. Check out the Deferred Documentation. Only .spawn utilizes the notify() method.


In lieu of a formal styleguide, take care to maintain the existing coding style. Add unit tests for any new or changed functionality. Lint and test your code using grunt.


Copyright (c) 2012 Dan Heberden
Licensed under the MIT license.