How to permanently set $PATH on Linux?

Goal

Very basic information that every Linux user needs to know - How to export $PATH . This variable contains all the paths which may have executables that will be recognized throughout the System. For example lets say you installed java. You want to compile a program and so you do javac TestClass.java and you get javac is not a recognized command. One way to resolve this is to do pathtojdk/bin/javac TestClass.java but this is not the best way. You can add path pathtojdk/bin to that $PATH environment variable and then you can access all commands in bin folder from anywhere in your System. So lets see how can we achieve this...

Getting Started...

So lets say I want to add following 3 paths to $PATH env variable

1. $HOME/mozilla/adt-bundle-linux/sdk/tools
2. $HOME/mozilla/adt-bundle-linux/sdk/build-tools
3. $HOME/mozilla/adt-bundle-linux/sdk/platform-tools

You can view your existing $PATH variable by just typing echo $PATH . To add it you can do the following. Execute the following on command line

export PATH=$PATH:$HOME/mozilla/adt-bundle-linux/sdk/tools:$HOME/mozilla/adt-bundle-linux/sdk/build-tools:$HOME/mozilla/adt-bundle-linux/sdk/platform-tools

then again you can check the $PATH variable using echo.

But wait a second. Restart the console and if you notice the exported PATH is gone. Yes it is lasts only for that console session. So lets see how can we export this $PATH permanently.

1. Edit your ~/.bashrc file and add the export line there.
2. Save the file.
3. Lastly execute source ~/.bashrc

Note : source command is basically to make your console aware of the changes that you have made in the file.

and thats it. Those PATHS should be in your $PATH environment variable permanently from there on.

Caution

• It's often considered a security hole to leave a trailing colon at the end of your bash PATH because it makes it so that bash looks in the current directory if it can't find the executable it's looking for.  
• Consider the scenario when you unpack a tarball, then cd to the directory you unpacked it in, then run ls---and then realize that the tarball had a malicious program called ls in it.
• There can be other, more nasty versions. For instance, creating a malicious script called sl and waiting for someone to mistype ls.   

Related Links

• How do I reload .bashrc without logging out and back in?

Getting Started with MongoDB

Introduction

From Wiki

MongoDB (from "humongous") is a cross-platform document-oriented database. Classified as a NoSQL database, MongoDB eschews the traditional table-based relational database structure in favor of JSON-like documents with dynamic schemas (MongoDB calls the format BSON), making the integration of data in certain types of applications easier and faster. Released under a combination of the GNU Affero General Public License and the Apache License, MongoDB is free and open-source software.

Getting Started

1. Download MongoDB from their website and install it. You have installer file for windows or zip file. Either way you should get MongoDB 2.6 Standard  folder installed. My folder location is C:\Program Files\MongoDB 2.6 Standard. You can find a bin file inside this folder. Add it to the %PATH% environment variable (windows) or export it by adding in .bashrc file(Linux).
2. Next open command prompt and run MongoDB server. To do so execute command
   
   mongod --dbpath C:\Users\athakur\Softwares\MongoDB
   
   Replace the path after --dbpath with your path. It basically says where your db files will be stored. If you do not provide db path your server will not start and will show that dbpath was missing.
   
   
   
   
   After starting the server with --dbpath
   
   
   
   
   You may be asked to allow network access to mongo db. Provide the required access.
   
   
   
3. Next start the client by typing
   
   mongoThat should open the Mongo shell.
   
   
   
   
   By default, mongo looks for a database server listening on port 27017 on the localhost interface. To connect to a server on a different port or interface, use the --port and --host options.
4. Lets create a new database. Type the following command
   
   use mydb
   
   and then type
   
   db
   
   This should show mydb database. Now try doing
   
   show dbs
   
   Nothing? Surprised? Don't be. It is the way Mongo DB behaves. MongoDB will not permanently create a database until you insert data into that database.
   
   Note : Unlike MySQL database you do not create tables and then insert data. Infact there is no relational model here. You simply switch db using use dbName syntax and add data. When you actually add the data the database is created.
   
   
   
5. Lets go ahead and insert some data in our database. First create documents doc1 and doc2 using
   
   doc1 = {name : "Aniket"}
   doc2 = {org : "openSourceForGeeks"}
   
   Then add these documents to the collection (lets call it testDataCollection) database using
   
   db.testDataCollection.insert( doc1 )
   db.testDataCollection.insert( doc2 )
   
       When you insert the first document, the mongod will create both the mydb database and the testDataCollection collection.
   
   You can view your collections by
   
   show collections
   
   Confirm that your testDataCollection collection is created.
   
   The mongo shell will return the list of the collections in the current (i.e. mydb) database. At this point, the only collection is testDataCollection . All mongod databases also have a system.indexes collection.
   
   Also confirm the database is created ( by show dbs).
   
   
   
6. Data Stored in MongoDB is essentially JSON. If you wish to see the data in the collection you can use command
   
   db.testDataCollection.find()
   
   
   
7. That;s all for basics of mongo db. We say how to create database, collections and insert data in it. We also saw how can we retrieve the data.

Important commands

1. db - shows current db in use
2. help - show help
3. cls - clear screen
4. exit - exit Mongo shell
5. show dbs - Show list of databases
6. use mydb - use some other database
7. show collections - Show all collection for the db. 

Important Links

• Getting Started with MongoDB
• Getting Started with MongoDB - Part 1
• Installing MongoDB in Mac(OSFG) 

Creating new developer profile on firefox using profilemanager.

Background

It all started when I thought of creating an addon for firefox. Basic setup requires you to set up a new profile to work on. I am not sure why this feature is known to few people developing addons for firefox. Basically you can create multiple profiles in firefox. That means if you  are sharing your computer with some other person you can have two different firefox profiles for each. Each profile has its own bookmarks, active logons etc. Both are mutually exclusive.

Logged into GMail? and friend wants to see his mail ? Use different profile. Keep one profile fixed for yourself.

So lets see how this is done.

Getting Started

1. Make sure there are no instances of firefox running or the below command won't work.
2. First add your firefox to your PATH environment variable (It is not necessary but if you are planning for experimenting with firefox like me I would suggest go ahead and do it.)
   
   
   
3. Next open your command prompt and type
   'firefox --profilemanager'.
   That should open a profile manager. In that you can create a new profile. I have named it 'developer'.
   
   
   
   
   
4. Once created you can launch any profile by the command
   'firefox -p developer'.
   If you want to run two profiles together you can do
   'firefox -no-remote -p default'.
   You need to use 'no-remote' argument.
   
   
   
   
5. You can also take backup up your profiles using MozBackup . You can download it from here.
   

Thats it with setting up the profile. If you only want to have exclusive profiles for use you are good with above. If you want to explore further look below -

Developer configurations

If you are looking ahead to  develop for mozilla firefox then you may want to set up certain configuration properties.

Open your browser with developer profile and enter 

about:config

in the address bar. You should see the following screen - 

Go ahead and select "I promise!" :). You should then get access to advanced configurations.

Set the properties as described in the Setting up an extension development environment.

How to display processing during Ajax request processing using jQuery

Goal

User interaction is very crucial. When you are making ajax calls to the server and response takes some time your webpage looks like hanged and user is clueless so as to what is happening. So it is a good approach to show some animated icon on the page during the request processing so that user can understand that the precessing is in progress.

On to the code.....

First, create an Ajax icon using the AjaxLoad site.

Then add the following to your HTML:

<img src="/images/loading.gif" id="loading-indicator" style="display:none" />

And the following to your CSS file:

#loading-indicator {
  position: absolute;
  left: 10px;
  top: 10px;
}

Lastly, you need to hook into the Ajax events that jQuery provides; one event handler for when the Ajax request begins, and one for when it ends:

$(document).ajaxSend(function(event, request, settings) {
  $('#loading-indicator').show();
});

$(document).ajaxComplete(function(event, request, settings) {
  $('#loading-indicator').hide();
});

Taken from source.

How to Use JSON Objects With Twitter Bootstrap Typeahead

Background

Bootstrap is a free collection of tools for creating websites and web applications. It contains HTML and CSS-based design templates for typography, forms, buttons, navigation and other interface components, as well as optional JavaScript extensions. (More on Wiki).

You can visit their official site for more details. You need to download it and add the css file and javascript file to your project. In this post i am going to cover how can we use JSON Object to autocomplete text fields.

To the Code.....

Add the following in your java script. You can put all typeahead calls in a single function and then call that function from your javascript in the HTML (or JSP) page.

var states = [];
var    map = {};
$('#search').typeahead({

    minLength: 0,

    source : function(query, process) {        

        states = [];

        map = {};
        //hardcoding this JSON but this would technically come from server
        var data = [
        {"stateCode": "CA", "stateName": "California"},
        {"stateCode": "AZ", "stateName": "Arizona"},
        {"stateCode": "NY", "stateName": "New York"},
        {"stateCode": "NV", "stateName": "Nevada"},
        {"stateCode": "OH", "stateName": "Ohio"}
    ];

    $.each(data, function (i, state) {
        map[state.stateName] = state;
        states.push(state.stateName);
    });

    process(states);
    },
    matcher: function (item) {
        //If user enters * show all possible entries
        if(this.query.trim().toLowerCase() == "*") {
            return true;
        }
        if (item.toLowerCase().indexOf(this.query.trim().toLowerCase()) != -1) {
            return true;
        }
    },
    updater: function (item) {
        //If you want to do something prior to updating value 
        selectedState = map[item].stateCode;
        return item;
    },
    sorter: function (items) {
        return items.sort();
    },
    highlighter: function (item) {
       // implementation
    },

});

Also you can override your typeahead class as follows for better looks

.typeahead {
max-height: 200px;
overflow-y: auto;
overflow-x: hidden;
}

Thats it for the autocomplete feature of twitter bootstrap. You can make ajax call to get the JSON data as follows

function getData(url, data, successCallback, errorCallback) {
    var requestType = "POST";
    var dataType = "json";
    make_ajax_call(url, data, requestType, dataType, successCallback, errorCallback);
}

function make_ajax_call(url, data, requestType, dataType, successCallback, errorCallback) {
    
    var request = {
        url : url,
        type : requestType,
        data : data,
        dataType : dataType,
        success : successCallback,
        error : errorCallback,
        async : false
    };
    jQuery.ajax(request);

}

You can import jquery using

<script src="http://code.jquery.com/jquery.js"></script>