export variables precedence over pipeline parameters

examples/buildspec_Example3/README.md

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+# buildspec_Example3
+
+This is an example Hello World project using Java to demonstrate the precedence of exported variables over pipeline parameters and build run arguments, with the [OCI DevOps service](https://www.oracle.com/devops/devops-service/)
+
+
+### Create External Connection to your Git repository 
+
+1. Create a [DevOps Project](https://docs.oracle.com/en-us/iaas/Content/devops/using/devops_projects.htm) or use and an existing project. 
+2. In your DevOps project, create an External Connection to your GitHub repository which holds your application.
+   - Create a Personal Access Token (PAT): https://docs.github.com/en/github/authenticating-to-github/keeping-your-account-and-data-secure/creating-a-personal-access-token
+   - In the OCI Console, Go to Identity & Security -> Vault and create a [Vault]( https://docs.oracle.com/en-us/iaas/Content/KeyManagement/Concepts/keyoverview.htm) in compartment of your own choice.
+   - Create a Master Key that will be used to encrypt the PATs. 
+   - Select Secrets from under Resources and create a secret using PAT obtained from GitHub account.
+   - Make a note of the OCID of the secret.
+   - Now, go to the desired project and select External Connection from the resources.
+   - Select type as GitHub and provide OCID of the secret under Personal Access Token.
+   - Finally, allow Build Service (dynamic group with DevOps Resources) to use a PAT secret by writing a policy in the root compartment as: ``` Allow dynamic-group dg-with-devops-resources to manage secret-family in tenancy```
+
+### Setup your Build Pipeline
+Create a new Build Pipeline to build, test and deliver artifacts from your GitHub Repository.
+
+### Managed Build stage
+In your Build Pipeline, first add a Managed Build stage
+1. The Build Spec File Path is the relative location in your repo of the build_spec.yaml . Leave the default, for this example.
+2. For the Primary Code Repository follow the below steps
+    - Select connection type as GitHub
+    - Select the external connection you created above
+    - Give the URL to the repo which contains your application.
+    - Select main branch.
+
+### Specify Pipeline parameter
+In your Build Pipeline , click on Parameters tab, and provide pipeline parameter as below:
+Name: var       Value: 19       Description: pipeline parameter
+Click on + tab to add this parameter
+
+<img src="pipeline_param.png"/>
+
+### Specify Exported variable
+In your build_spec.yaml, specify "var" under exportedVariables section and in commands set the value of this variable to 22.
+
+### Run your Build with Build run parameter using oci-curl
+
+
+#### Setup oci-curl on localhosr
+To configure access for oci-curl for the first time, follow this link https://confluence.oci.oraclecorp.com/display/DLCBLD/HOWTO%3A+Setup+oci-curl+on+localhost.
+
+
+#### make a createBuildRun.json file and paste the followinf contents in it (BuildRun argument as var:23)
+```
+    {
+    "displayName": "build#1",
+    "buildPipelineId": <PIPELINE_ID>,
+    "commitInfo": {
+    "repositoryUrl": "string",
+    "repositoryBranch": "string",
+    "commitHash": "string"
+    },
+    "buildRunArguments": {
+        "items": [
+        {
+            "name": "var",
+            "value": "23"
+        }
+        ]
+    },
+    "freeformTags": {},
+    "definedTags": {}
+    }
+```
+
+#### Run your pipeline using oci-curl
+```oci-curl devops-beta.us-ashburn-1.oci.oc-test.com POST createBuildRun.json "/20210630/buildRuns"```
+
+
+
+### Check the build context after build run execution gets completed
+1. Go to build history
+<img src="build_history.png" />
+2. Copy your Build Run OCID from current Build run
+3. At the end of build run execution run the following command in your terminal
+   oci-curl devops-beta.us-ashburn-1.oci.oc-test.com GET "/20210630/buildRuns/<BUILD_RUN_ID>"
+
+  , you will find that the value of var changed to 22, which means the exportedVariable overrides both pipeline and build run parameter.
+<img src="build_context.png" />

examples/buildspec_Example3/build_spec.yaml

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+version: 0.1
+component: build
+timeoutInSeconds: 6000
+runAs: root
+shell: bash
+env:
+  exportedVariables:
+    - var
+
+steps:
+  - type: Command
+    name: "Github Build Source"
+    timeoutInSeconds: 400
+    command: |
+      echo "VALUE OF VAR BEFORE "$var
+      cd src/main/java/org/example
+      javac HelloWorld.java
+      echo "COMPILED SUCCESSFULLY"
+      java HelloWorld
+      var=22
+      echo "VALUE OF VAR AFTER "$var
+
+outputArtifacts:
+  - name: outputEg3
+    type: BINARY
+    location: src/main/java/org/example/HelloWorld.class

examples/buildspec_Example3/src/main/java/org/example/HelloWorld.java

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+public class HelloWorld {
+    public static void main(String[] args) {
+        System.out.println("hello world!!");
+    }
+}