Merge pull request jenkinsci#66 from mramanathan/cfgfile_provider

configFile Provider plugin usage

Author: R. Tyler Croy

pipeline-examples/configfile-provider-plugin/README.md

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+[configFile Provider plugin] (https://plugins.jenkins.io/config-file-provider) enables provisioning of various types of configuration files. Plugin works in such a way as to make the configuration available for the entire duration of the build across all the build agents that are used to execute the build.
+
+Common scenarios that demand the usage of configuration files:
+
+- Provide properties that can be consumed by the build tool
+- Global settings that override local settings
+- Details of credentials needed to access repos
+- Inputs to generate binary images that need to be tailored to specific architectures 
+
+The example shows simple usage of configFile Provider plugin and howto access it's contents.

pipeline-examples/configfile-provider-plugin/configFileProvider.groovy

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+#!groovy
+
+node {
+    stage('configFile Plugin') {
+
+        // 'ID' refers to alpha-numeric value generated automatically by Jenkins.
+        // This code snippet assumes that the config file is stored in Jenkins.
+
+        // help to assign the ID of config file to a variable, this is optional 
+        // as ID can be used directly within 'configFileProvider' step too.
+        def mycfg_file = '<substitute-alpha-numeric-value-cfgfille-here-within-quotes>'
+
+        // whether referencing the config file as ID (directly) or via user-defined 
+        // variable, 'configFileProvider' step enables access to the config file
+        // via 'name' given for the field, 'variable:'
+        configFileProvider([configFile(fileId: mycfg_file, variable: 'PACKER_OPTIONS')]) {
+            echo " =========== ^^^^^^^^^^^^ Reading config from pipeline script "
+            sh "cat ${env.PACKER_OPTIONS}"
+            echo " =========== ~~~~~~~~~~~~ ============ "
+ 
+            // Access to config file opens up other possibilities like
+            // passing on the configuration to an external script for other tasks, like,
+            // for example, to set generic options that can be used for generating 
+            // binary images using packer.
+            echo " =========== ^^^^^^^^^^^^ Reading config via Python... "
+            sh "python build_image.py ${env.PACKER_OPTIONS}"
+            echo " =========== ~~~~~~~~~~~~ ============ "
+        }
+    }
+}