How to set environment variable for a app running on Openshift Online?

Resolution

• From a client system, one can set the environment variable using the following command:

# rhc env set test=test --app myphpapp
Setting environment variable(s) ... done

• SSH to the app and check if the env variable value has been set inside the gear:

# rhc ssh myphpapp
Connecting to 523c50ff5004464b1c000001@myphpapp-anande.rhcloud.com ...

    *********************************************************************

    You are accessing a service that is for use only by authorized users.  
    If you do not have authorization, discontinue use at once. 
    Any use of the services is subject to the applicable terms of the 
    agreement which can be found at: 
    https://www.openshift.com/legal

    *********************************************************************

    Welcome to OpenShift shell

    This shell will assist you in managing OpenShift applications.

    !!! IMPORTANT !!! IMPORTANT !!! IMPORTANT !!!
    Shell access is quite powerful and it is possible for you to
    accidentally damage your application.  Proceed with care!
    If worse comes to worst, destroy your application with "rhc app delete"
    and recreate it
    !!! IMPORTANT !!! IMPORTANT !!! IMPORTANT !!!

    Type "help" for more info.


    ***  This gear has been temporarily unidled. To keep it active, access
    ***  your app @ http://myphpapp-anande.rhcloud.com/

[myphpapp-anande.rhcloud.com 523c50ff5004464b1c000001]\> echo $test
test

• The Environment Variable value can also be checked (from the client system) without SSH'ing to the gear:

# rhc env list --app myphpapp
test=test

OR 

# rhc env show test --app myphpapp
test=test