I have developed a module to execute a generic command using the child_process spawn.
I have two api in this module a single command execution api, CommandLine.execute and a multiple commands execution api, CommandLine.executeCommands, that I call in this way:
// commandItemsArray is a list of commands list
// that is an array of [command, options, arguments]
commandItemsArray = [ ['ls','-l','./'], ['ls','-a','./'] ];
command.executeCommands( commandItemsArray
, function(results) {
console.log( results );
}
, function(error) {
console.log( error );
});
or
commandItemsArray = [ ['ls','-l','./'] ];
command.executeCommands( commandItemsArray
, function(results) {
console.log( results );
}
, function(error) {
console.log( error );
});
This module is standalone (relies only on node built-in modules) and that's the code:
(function() {
var CommandLine;
CommandLine = (function() {
var cp = require('child_process');
/**
* Command line helper module
* This module is standalone
* @author: loretoparisi at gmail dot com
*/
function CommandLine(options,logger) {
var self=this;
// defaults
this._options = {
// true to debug
debug : false,
// true to show errors
error : true
};
// override defaults
for (var attrname in options) { this._options[attrname] = options[attrname]; }
/**
* Wrappar around Promise.all
*/
this.PromiseAll = function(items, block, done, fail) {
var self = this;
var promises = [],
index = 0;
items.forEach(function(item) {
promises.push(function(item, i) {
return new Promise(function(resolve, reject) {
if (block) {
block.apply(this, [item, index, resolve, reject]);
}
});
}(item, ++index))
});
Promise.all(promises).then(function AcceptHandler(results) {
if (done) done(results);
}, function ErrorHandler(error) {
if (fail) fail(error);
});
}; //PromiseAll
}
/**
* Execute a command
* @param commands Array of command, options, arguments
* @example ['ls','-l','./']
* @param resolve Block success block
* @param reject Block rejection block
*/
CommandLine.prototype.execute = function(command, resolve, reject) {
var self=this;
resolve = resolve || function(results) {};
reject = reject || function(error) {};
return self.ExecutionBlock(item, index, resolve, reject);
} //execute
/**
* Execute a list of commands
* @param commands Array of command array of of command, options, arguments
* @example [ ['ls','-l','./'], ['ls', '-a', './'] ]
* @param resolve Block success block
* @param reject Block rejection block
*/
CommandLine.prototype.executeCommands = function(commands, resolve, reject) {
var self=this;
resolve = resolve || function(results) {};
reject = reject || function(error) {};
/**
* Execution block handler
*/
var ExecutionBlock = function(item, index, resolve, reject) {
var executable = item[0]; // first elem is command
var options = item.splice(1,item.length);
if(self._options.debug) {
console.log( item );
console.log( executable, options.join(' ') );
}
var data = new Buffer("",'utf-8');
// LP: now spawn the power!
var child = cp.spawn(executable, options);
// Listen for an exit event:
child.on('exit', function(exitCode) {
return resolve( { data : data.toString('utf-8'), code : exitCode } );
});
// Listen for stdout data
child.stdout.on('data', function(_data) {
console.log( ( new Buffer(_data)).toString() );
data = Buffer.concat([data, _data]);
});
// child error
child.stderr.on('data',
function(data) {
if(self._options.error) {
console.log('err data: ' + data);
}
// on error, kill this child
child.kill();
return reject(new Error(data.toString()));
}
);
} //ExecutionBlock
self.PromiseAll(commands
, function(item, index, _resolve, _reject) {
ExecutionBlock(item, index, _resolve, _reject);
}
, function(results) { // aggregated results
// all execution done here. The process exitCodes will be returned
// array index is the index of the processed that exited
return resolve(results);
}
, function(error) { // error
return reject(error);
});
} //executeCommands
return CommandLine;
})();
module.exports = CommandLine;
}).call(this);
I'm using a Promise.all to spawn multiple processes, wait execution, and collect stdout output in a node Buffer like:
// Listen for stdout data
child.stdout.on('data', function(_data) {
console.log( ( new Buffer(_data)).toString() );
data = Buffer.concat([data, _data]);
});
At the very exit child event I return the child process exit code and data in a struct:
child.on('exit', function(exitCode) {
return resolve( { data : data.toString('utf-8'), code : exitCode } );
});
While, executing some commands has no problem, executing shell commands like ls give me back unexpected results such as I do not get the results expected to be in the callback of PromiseAll method, and I do not understand why.
self.PromiseAll(commands
, function(item, index, _resolve, _reject) {
ExecutionBlock(item, index, _resolve, _reject);
}
, function(results) { // aggregated results
// all execution done here. The process exitCodes will be returned
// array index is the index of the processed that exited
return resolve(results);
}
, function(error) { // error
return reject(error);
});
One doubt is about the node Buffer concatenation explained here, that seems to be tricky:
var data = new Buffer("",'utf-8');
// LP: now spawn the power!
var child = cp.spawn(executable, options);
// Listen for an exit event:
child.on('exit', function(exitCode) {
return resolve( { data : data.toString('utf-8'), code : exitCode } );
});
// Listen for stdout data
child.stdout.on('data', function(_data) {
console.log( ( new Buffer(_data)).toString() );
data = Buffer.concat([data, _data]);
});
I will expect { data : data.toString('utf-8')} to keep the whole buffer chained as string, but I wonder if the utf-8 is the right encoding for the stdout output, supposed that we are talking about of shell commands of course.
