UI

How to fork and pipe multiple processes on Linux

The C code here is used for reference of how to pipe 3 separate children processes. It can be improved to support a dynamic amount of processes and corresponding pipes and system calls.

// This program is an example of how to run a command such as
// ps aux | grep root | grep sbin
// using C and Unix.
// pipe_example.c

#include 
#include 
#include 

int pid;
int pipe1[2];
int pipe2[2];

void exec1();
void exec2();
void exec3();

int main()
{

	// create pipe1
	if (pipe(pipe1) == -1)
	{
		perror("bad pipe1");
		exit(1);
	}

	// create pipe2
	if (pipe(pipe2) == -1)
	{
		perror("bad pipe2");
		exit(1);
	}

	// fork (ps aux)
	if ((pid = fork()) == -1)
	{
		perror("bad fork1");
		exit(1);
	}
	else if (pid == 0)
	{
		// stdin --> ps --> pipe1
		exec1();
	}
	// parent

	// fork (grep root)
	if ((pid = fork()) == -1)
	{
		perror("bad fork2");
		exit(1);
	}
	else if (pid == 0)
	{
		// pipe1 --> grep --> pipe2
		exec2();
	}
	// parent

	// close unused fds
	close(pipe1[0]);
	close(pipe1[1]);

	// fork (grep sbin)
	if ((pid = fork()) == -1)
	{
		perror("bad fork3");
		exit(1);
	}
	else if (pid == 0)
	{
		// pipe2 --> grep --> stdout
		exec3();
	}
	// parent
}

void exec1()
{
	// input from stdin (already done)
	// output to pipe1
	dup2(pipe1[1], 1);
	// close fds
	close(pipe1[0]);
	close(pipe1[1]);
	// exec
	execlp("ls", "ls", NULL);
	// exec didn't work, exit
	perror("bad exec ls");
	_exit(1);
}

void exec2()
{
	// input from pipe1
	dup2(pipe1[0], 0);
	// output to pipe2
	dup2(pipe2[1], 1);
	// close fds
	close(pipe1[0]);
	close(pipe1[1]);
	close(pipe2[0]);
	close(pipe2[1]);
	// exec
	execlp("grep", "grep", "c", NULL);
	// exec didn't work, exit
	perror("bad exec grep c");
	_exit(1);
}

void exec3()
{
	// input from pipe2
	dup2(pipe2[0], 0);
	// output to stdout (already done)
	// close fds
	close(pipe2[0]);
	close(pipe2[1]);
	// exec
	execlp("grep", "grep", "y", NULL);
	// exec didn't work, exit
	perror("bad exec grep y");
	_exit(1);
}

This code also works on Unix/Mac.
Compile with gcc pipe_example.c -o pipe_example.o
Run with ./pipe_example.o

Creating and Opening PDF on Ionic 1 on iOS

Recently I ran into an issue using the PdfMake on Ionic 1 on iOS. It works fine on the browser with a simple download or open command but not on the actual device.

Install the cordova libraries:

cordova.plugins.fileOpener2
cordova-plugin-file

Download the pdfmake javascript files and include them in your index.html

<script src='build/pdfmake.min.js'></script>
<script src='build/vfs_fonts.js'></script>

The code:

  var self = this ; // defined on top of the file

  var docDefinition = { content: 'This is an sample PDF printed with pdfMake' };

            self.pdfObj = pdfMake.createPdf(docDefinition);

            if (window.cordova) {
                self.pdfObj.getBuffer(function (buffer) {
                    var blob = new Blob([buffer], { type: 'application/pdf' });
                    // Save the PDF to the data Directory of our App
                    $cordovaFile.writeFile(cordova.file.dataDirectory, 'myletter.pdf', blob, { replace: true }).then(function () {
                        // Open the PDf with the correct OS tools
                        cordova.plugins.fileOpener2.open(cordova.file.dataDirectory + 'myletter.pdf', 'application/pdf');
                    })
                });
            }



Setup Config.xml


In your config.xml make sure you have the file settings


<preference name="AndroidPersistentFileLocation" value="Compatibility" />


<preference name="iosPersistentFileLocation" value="Library" />

How To Use Ionic & Angular q Promises?

The Deferred API

A new instance of deferred is constructed by calling $q.defer().

The purpose of the deferred object is to expose the associated Promise instance as well as APIs that can be used for signaling the successful or unsuccessful completion, as well as the status of the task.

Methods

resolve(value) – resolves the derived promise with the value. If the value is a rejection constructed via $q.reject, the promise will be rejected instead.

reject(reason) – rejects the derived promise with the reason. This is equivalent to resolving it with a rejection constructed via $q.reject.

notify(value) – provides updates on the status of the promise’s execution. This may be called multiple times before the promise is either resolved or rejected.
Properties

promise – {Promise} – promise object associated with this deferred.

// for the purpose of this example let's assume that variables `$q` and `okToGreet`
// are available in the current lexical scope (they could have been injected or passed in).

function asyncGreet(name) {
  var deferred = $q.defer();

  setTimeout(function() {
    deferred.notify('About to greet ' + name + '.');

    if (okToGreet(name)) {
      deferred.resolve('Hello, ' + name + '!');
    } else {
      deferred.reject('Greeting ' + name + ' is not allowed.');
    }
  }, 1000);

  return deferred.promise;
}

var promise = asyncGreet('Robin Hood');
promise.then(function(greeting) {
  alert('Success: ' + greeting);
}, function(reason) {
  alert('Failed: ' + reason);
}, function(update) {
  alert('Got notification: ' + update);
});

This code example was taken from Angular Documentation page: https://docs.angularjs.org/api/ng/service/$q

Style Ion-Radio checkbox in Ionic with CSS

Recently I had the trouble of changing the default radio checkbox in ionic. Here is the CSS of how to do this:

.list .item-radio .item-content {
  background-color: black;
  color: white;
}
.list .item-radio .radio-icon {
  background-color: black;
  color: white;
}
.item-radio input:checked + .radio-content .item-content {
    /* style the item content when its checked */
    background: black; 
}

Terrible Car Design Killed Anton Yelchin.

It is this Jeep vehicle that killed the ‘Star Trek’ actor Anton Yelchin. This very irresponsible car design by Chrysler is what caused the actor’s death without a doubt. There was no real need to make this shifter all electronic. Absolutely nothing is gained by this software solution of a hardware problem. Terrible human factors engineering all around.

How to Hide Specific Ionic Tabs in Angular

How to Hide Specific Ionic Tabs in Angular? It turns out ionic does not support this functionality by default although I think it should, but luckily it’s not that complicated.

Here are the 3 simple steps:

1. In your tabs.html add this ng-class

<ion-tabs ng-class="{'tabs-item-hide': hideTabs}">

</ion-tabs>

2. Add ‘hide-tabs’ in your views where you want to hide the tabs

<ion-view hide-tabs> 

</ion-view>

3. In your app.js add the directive to hide tabs

.directive('hideTabs', function($rootScope) {
    return {
        restrict: 'A',
        link: function($scope, $el) {
            $rootScope.hideTabs = true;
            $scope.$on('$destroy', function() {
                $rootScope.hideTabs = false;
            });
        }
    };
})

The hide-tabs directive will hide the tab on whichever ion-view you set it to.

Ionic App Starter Templates on Noodl.io and Ionic Marketplace

I recently published some of my Ionic Starter Templates that should speed up your new hybrid app development on Noodl.io and Ionic Market. All starters have been tested on both iOS and Android.

 

Screen Shot 2016-01-10 at 3.27.51 PMIonic Geolocation – A quick way to start a new geolocation enabled app

Ionic Phonebook – A very easy way to start your phonebook & contacts app

Ionic OAuth – A full app with a node.js backend to support user creation, session, login & social login

Ionic Login Session – A full stack app with node.js backend without the social login support

Also please leave a rating if you get one! many thnx =)